Sec 2E Physics

Post from Mrs Chiam

2008-06-20T18:30:00.000-07:00

To all:

The deadline for Part 1 of the project is over.

Some of you have sent your files in 07 format. Do give me some time to access as currently my laptop cant open them. need to use another computer to open that.
So dont worry about that.

Some of you have not followed my instructions. No acknowledgments, incorrect length of reflection. Some just copied wholesale from the website without understanding fully wat was being written. Some just took from the textbook which was really short. Marks would be deducted accordingly if so.

Late submissions from now onwards will result in loss of marks except for those who have approached me personally due to valid reasons. No submissions will cause a ZERO MARK to be awarded.

Note: some of your pics arent uploaded in the blog. But pls make use of them when you get together in your groups to design the poster. Thanks

A gentle reminder: This project will be counted as a CA mark in Term 3. No submission or late submission will result in YOU getting 0 marks in Term 3. TAKE NOTE!

Refraction of Light by 2E2 Chen Jing

2008-06-20T09:33:00.000-07:00

!what do you learn about that particular topic?

I learn that the The bending of light that occurs when light passes from one transparent material to another is called refraction of light.light bends because its speed hanges as it moves from one transparent material to another.

light travels slower in more dense materials than in less dense materials.therefore light travels slower in glass than in air.

and i know many effects of refraction of light.such as we can use refraction of light to made the words appear to be nearer to the surface of the glass than they actually are.

From:textbook resource!

summarise the key points of that topic.
Refraction is the bending of light that takes place at a boundary between two materials having different indices of refraction.

Refraction is due to a change in the speed of light as it passes from one medium to another. The change in direction of the ray (represented by the heavy line in each diagram) is what is meant by the term refraction, which just means ¡°bending¡± or ¡°breaking.¡±

From:http://mintaka.sdsu.edu/GF/explain/optics/refr.html!

anything interesting to add?I

n 1621, a Dutch physicist named Willebrord Snell (1591-1626), derived the relationship between the different angles of light as it passes from one transperent medium to another.

When light passes from one transparent medium to another, it bends according to Snell's law which states:Ni * Sin(Ai) = Nr * Sin(Ar),

where:Ni is the refractive index of the medium the light is leaving,Ai is the incident angle between the light ray and the normal to the meduim to medium interface,Nr is the refractive index of the medium the light is entering,Ar is the refractive angle between the light ray and the normal to the meduim to medium interface.

From:http://www.ps.missouri.edu/rickspage/refract/refraction.html

Refraction of Light by 2E2 Tan Chew Mei

2008-06-20T09:31:00.000-07:00

i.What is refraction of light ?

Refraction is the change in direction of a wave due to a change in its speed. This is most commonly seen when a wave passes from one medium to another. Refraction of light is the most commonly seen example, but any type of wave can refract when it interacts with a medium, for example when sound waves pass from one medium into another or when water waves move into water of a different depth. Refraction is also described by Snell’s Law.

ii.When does it happen? How will light bend ?

In optics, refraction occurs when light waves travel from a medium with a given refractive index to a medium with another. At the boundary between the media, the wave's phase velocity is altered, it changes direction, and its wave length increases or decreases but its frequency remains constant. For example, a light ray will refract as it enters and leaves glass; understanding of this concept led to the invention of lenses and the refracting telescope.

iii. What is refractive index ?

Refraction can be seen when looking into a bowl of water. Air has a refractive index of about 1.0003, and water has a refractive index of about 1.33.

Iv. Effect of refraction ?

refraction can make objects appear closer than they are, it is responsible for allowing water to magnify objects. First, as light is entering a drop of water, it slows down. If the water's surface is not flat, then the light will be bent into a new path. This round shape will bend the light outwards and as it spreads out, the image you see gets larger.

Refraction of Light by 2E1 The Su Zin

2008-06-20T09:29:00.000-07:00

After doing research about this topic, I have learnt more concerning with the topic: refraction such as its laws and rules and also about refractive index.

1)Refraction
Refraction refers to the change in direction of light when it moves from one transparent medium into another transparent material which causes it to travel at a different speed.

Light slows down

Visible light is electromagnetic radiation or waveform. The speed or velocity of light in a vacuum is about 186,000 miles per second or 300,000 kilometres per second. The velocity of light or other electromagnetic radiation is typically slower when it passes through a transparent material. For example, the speed of light in water is about 140,000 mi/sec or 226,000 km/sec.

2)Refraction Rules When visible light passes through a transparent material such as glass and water, its velocity(speed) changes according to the index of refraction of the material. The index of refraction of air is about 1.00 and that of water is 1.33. When the beam of light enters water at an angle, it is bent or refracted as a result of the decrease in velocity.
Light is refracted inward when entering medium of higher index of refraction
Light is refracted outward when entering medium of lower index of refraction
The bending occurs because light travels more slowly in a denser medium.

Why does the light beam bend?
Considering a group of soldiers marching into a muddy field at an angle to their direction of travel can explain how a beam of light will be refracted. As the soldiers try to stay in a line, the direction of travel would bend because marching in mud would slow them down, starting with the first group to enter the field. Then, as they leave the muddy area, they go to their original speed, thus bending the direction of travel again. The original direction and the final direction are parallel but displaced.
The same thing happens when a beam of light enters a transparent material at an angle.

Example of how light is refracted when passes through different medium.

3 )INDEX OF REFRACTION
Refractive index is a number which indicates the power of refraction of a given medium relative to a previous medium. The absolute refractive index of a medium is the speed of light in a vacuum (air) divided by the speed of light in that medium.
Symbol is “n”. The larger the index ,the smaller the speed of light.
n = c/v

4)THE EFFECTS OF REFRACTION
Refraction has some unusual effects in everyday life.
-When a submerged object is viewed from above the surface of water, it appears closer to the surface than it is. This is due to light rays from the object being bent away from the normal as they pass out of the water (the more dense medium) into air (the less dense medium).
-The ratio of the real depth of the object to its apparent depth equals the refractive index of water.

Here are some examples of the EFFECTS:

eg1 - Apparent Depth in Water
In the above diagram, the chest seems to be nearer to the surface, but it is not. Refraction causes the chest to appear nearer to the surface than it actually is when it is in transparent material, water .

When you look at something under the water, not only the position of the object is not located at the place you though it was. The shape of the object is also changed. Location of the image and its shape are all depend on the location you view it.

eg2- In this diagram, the straw seems bent in the glass.
Refraction causes point X to appear nearer to the surface at Y so we see that that the straw appears to bend nearer to the surface of the water. This is one of the effect of refraction.

Eg.3 Pencil in water glass

You can also see this effect by putting a pencil in a glass of water. It appears as if the pencil is broken, but it is just because of the refraction of light.
The light from the pencil is refracted as it passes from the water to the glass to air, causing it to be displaced. Since the surface of the glass is curved, the water in the glass also acts as a magnifying glass, slightly enlarging the pencil.

So here is the link for mini short quiz, very simple quiz. =)
http://www.school-for-champions.com/science/light_refraction.htm#Mini-quiz

Acknowledgement
1 . http://sol.sci.uop.edu/~jfalward/refraction/refraction.html
2.http://sg.answers.yahoo.com/question/index;_ylt=ApfjYqHaykzhEnCDtDjBpjYh4wt.;_ylv=3?qid=20070902013243AA3gdvF
3. http://www.school-for-champions.com/science/light_refraction.htm
http://www.phy.ntnu.edu.tw/ntnujava/
4. The Usborne Illustrated Dictionary Of Physics

Colours of Light by 2E1 Jason

2008-06-20T09:27:00.000-07:00

Colour:
Colour is the visual perceptual property corresponding in humans to the categories called red, yellow, blue, black, etc. Colour derives from the spectrum of light interacting in the eye with the spectral sensitivities of the light receptors.

White light is a mixture of different colours and when it passes through a glass prism, the light splits up into the colours you see in a rainbow. Spectrum, (white light) consists of Red, Orange, Yellow, Green, Blue, Indigo and Violet. The separation of splitting of white light into its separate colours is known as ‘Dispersion’. The colours of the spectrum can be recombined by using a second prism or spinning a colour wheel, we can get white light.

Mixing Coloured Lights
The primary colours of light are red, blue, and green. You can get white light or any other colour by mixing just three colours. If you mix two primary colours at a time, you will get magenta, yellow, and cyan.

Colour Filters
Colour filter is the clear plastic or glass which only lets through some of the colours meanwhile the other colours is being absorbed.
When white light (spectrum) shines on a coloured object, some of the colours in the spectrum are reflected and some are being absorbed. We can see the colour that is reflected light.

Credits:
http://en.wikipedia.org/wiki/Colour
http://wolfstone.halloweenhost.com/Lighting/colmix_ColorMixing.html
Explore Your World with SCIENCE DISCOVERY 2 [Chapter 8.4, colour]

Colours of Light by 2E4 Jeremy Lim

2008-06-20T09:25:00.000-07:00

In this topic I have learn about how colours are produce , what is dispersion of light and to recombine colours back after spitting them and also what is the effect of mixing colours as well as what is primary colours.

White light which is also known as ordinary light actually is a mixture of different colours. And when that white light pass through a glass prism the light actually spits up into 7 different colours and that process is call dispersion.

The spectrum consist of 7 beautiful colours, they are red, orange, yellow, green, blue, indigo, violet. It is also difficult to say when one colours ends or start as these colours merge into one another gradually.

The reason why there is always (maybe) a rainbow after a shower of rain is because the raindrops act like small prism and when sunlight passes through them …. They form the colours of the spectrum.

And since we are able to separate those seven colours from the spectrum, thus we are also able to rejoin the seven colours back into white light. And in order to do that is 2 ways.

The first way is to add in another prism or to spin a colour wheel and another
name for the colour wheel is call a Newton disc.

Lights of different colours can be mixed together to produce other colours and in fact white light and light of other colours can be obtained by mixing 3 colours, these colours are red, blue , green. These colours are called primary colours.

Here are the *formula* of colours, red + blue = magenta, red+ green = yellow, blue + green = cyan. And by adding the 3 primary we get white colours.
Clear plastic or glass only let through some colours and the other colours are absorbed are call colour filter. When white light shines on a coloured object, some colour are reflected and some are absorbed.

To end my project work, I want to say that the colour of an object is the colour of the light that is reflected from it into our eyes. And if no light is reflected the object would be black. Black is not a colour it is just something that indicates the absence of light.

Text book resource*

Refraction of Light by 2E1 Shahir

2008-06-20T09:23:00.000-07:00

For thousands of years, people have noticed that a straight stick placed obliquely in water appears to be broken at an angle where it enters the water. This is the origin of the term "refraction," which means literally "broken back."

Refraction is the change of light that changes direction when it passes from one medium to another.

refraction occurs when light waves travel from a medium with a given refractive index to a medium with another.

At the boundary between the media, the wave's phase velocity is altered, it changes direction, and its wavelength increases or decreases but its frequency remains constant.

For example, a light ray will refract as it enters and leaves glass.the understanding of this concept led to the invention of lenses and the refracting telescope

from a less dense material to a denser material, light will slows down and refracted towards the normal, while from denser material into a less dense material, light speeds up and is refracted away from the normal.

The refractive index of a transparent optical medium, also called the index of refraction, is the factor by which the phase velocity is decreased relative to the velocity of light in vacuum, assuming linear propagation

effects of refraction are : -it causes an object to be nearer than it actually is when a transparent material is on top - a stick will appear to be bent inside a bearker filled with water.

From this topic, i have learned that refraction happens in our everyday life. It causes effects that are very unusual and refraction is an interesting topic to learn.

key points : -refraction happens when light changes direction when it passes from one medium to another -it causes effects that are unusual.

Reflection of light by 2E3 Huang Yue

2008-06-20T09:21:00.000-07:00

What is reflection ???????
The bouncing of light off a mirror surface is called reflection.

Types of reflection?????
There are two types of reflection --regular reflection , diffuse reflection.
--When a parallel beam of light hits a smooth surface,it would be reflected as a parallel beam .This is called regular reflection.

--When a beam of light hits a rough surface,the individual rays are reflectedin different directions,then no image formed .This types of reflection is called diffuse reflection.

Uses of reflection of light,examples?

Uses of plane mirrors -----
—— the rear of a view mirror of a car can helps to see traffic behind the car.
——plane mirrors on walls makes a room brighter.
——people use plane mirrors to check their appearance.

Uses of curved mirrors----
——security mirrors are used in shops.
——blind corner mirrors helped driver to see objects around the corner.
——a concave mirror is used to reflect light into microscope.

Acknowledgements:
----Explore your world with science discovery 2
-----http://images.google.cn/imgres?imgurl=http://id.mind.net/~zona/mstm/physics/light/rayOptics/reflection/r1.jpg&imgrefurl=http://id.mind.net/~zona/mstm/physics/light/rayOptics/reflection/reflection1.html&h=300&w=400&sz=14&hl=zh-CN&start=17&um=1&tbnid=vcnBWStV9c6jCM:&tbnh=93&tbnw=124&prev=/images%3Fq%3Dreflection%2Bof%2Blight%26um%3D1%26complete%3D1%26hl%3Dzh-CN%26rlz%3D1T4XNLA_zh-CNSG277SG277%26sa%3DX

Colours of Light by 2E4 Jun Min Jung

2008-06-20T09:19:00.000-07:00

How are colours being produced?
Colours are produced because of sun light(white light).

What is Dispersion of light?
The speed of light is slower in various than it is in a vacuum or outer space. When the light passes into a material at an angle, the light beam is bent or refracted according to Snell’s Law and the index of retraction of the material. But also, the speed of light through a material varies slightly with the wavelength or frequency of the light. Thus, each wavelength is refracted at a slightly different angle when passing through a material at an angle. This spreading out of the beam of light is called dispersion. This can be seen when sunlight passes through a glass prism.

How to get rainbow colours and to recombine colours again?
Rainbow is formed when sunlight (white light) passes through raindrops. Tiny droplets of water refract the white light from the sun and create a spectrum of colours similar to what happen in a prism. Since the droplets are spheres, the light is reflected internally in the droplets and the rainbow returns toward the direction of the light.

Since white light consists of seven colours, we should be able to get white light again by combining the colours together. There are two ways to recombine the colours.
• By using a second prism: When another prism is placed, the colours recombine.
• Spinning a colour wheel (also called a Newton’s disc\): When the wheel is turned quickly, the colours appear to mix and the wheel looks white.

What is primary colours?
Light of different colours can be mixed together to produce other colours. In fact, white light and other light of colours – red, blue and green. These three colours are called the primary colours.

Effects of Mixing of Colours
Mixing the primary colours two at a time gives the following colours:
• red + blue = green
• red + green = yellow
• blue + green = cyan
Mixing all three primary colours gives white light. That is:
• red + blue + green = white

http://www.school-for-champions.com/science/light_dispersion.htm
Textbook - p.128~p.130

Colours of Light by 2E1 Vaishnavi

2008-06-20T09:17:00.000-07:00

In this essay I am going to explain about our physics project. My topic was colours. From the project we have understood many things about colours.

Colour is simply light of different wavelengths and frequencies and light is just one form of energy that we can actually see.

The three primary colours are red, green and blue. Colour comes from light.

To see the colour physically we need to have a prism. When light from the sun passes through a prism, the light is split into the seven visible colours by refraction.

Refraction is caused by the change in speed experienced by a wave of light when it changes medium. The amount of energy in a given light wave is proportionally related to its frequency, thus a high frequency light wave has a higher energy than that of a low frequency.

Each colour has its own particular wavelength and frequency. Each colour can be measured in units of cycles or waves per second. The frequency of a wave is determined by the number of complete waves, or wavelengths, that pass a given point each second.

Higher frequency colours are - violet - indigo - blue lower frequency colours are - yellow - orange - red.
A high frequency light wave has a higher energy than that of a low frequency light wave.

Refraction of Light by 2E1 Fatima

2008-06-20T09:15:00.000-07:00

What is refraction?
Refraction is the bending of a light when it passes from one transparent medium into another.

When and how does it happen?
Light changes direction because light travels at different speeds in different substances, causing it to be bent when it changes from one substance to another.

The degree of refraction depends in part on the angle at which the light hits the surface of a material. A line perpendicular to that surface is called the normal. The angle between the incoming light ray and the normal to the surface is called the angle of incidence. The angle between the refracted ray and the normal is called the angle of refraction. The angle of refraction cannot exceed 90°.
A ray of light refracts or deviates from its original path as it passes from one optical medium to another because the speed of light changes.

Refractive Index?
The amount of refraction can be found using the refractive index.
The speed at which light travels may change as it passes from one medium to another. Different substances will cause different changes to the speed of light. For example, glass slows light more than water.

To find the effect of a substance we can calculate its refractive index. This is a ratio of the speed of light in air or vacuum and the speed of light in the substance.

refractive index = speed of light in air/speed of light in substance

For example, the speed of light in air is 300,000 km/s and in glass it travels at about 200,000 km/s. Its refractive index is therefore 1.5. Water, however, has a refractive index of 1.33. This means that light rays are refracted more when they enter glass than when they enter water.

Effects of Refraction?
The effects of refraction:
1. Make things appear to be nearer
2. make objects in water appear to be bent
the pencil appears to be bent because of refraction

DK Reference Encyclopedia
http://www.tutorvista.com/content/physics/physics-ii/light-refraction/refraction-light.php
http://images.google.com.sg/

Electricity by 2E1 Darren Tan

2008-06-20T09:14:00.000-07:00

What is electricity?
Electricity is a form of energy. Electricity is the flow of electrons. All matter is made up of atoms, and an atom has a center, called a nucleus. The nucleus contains positively charged particles called protons and uncharged particles called neutrons. The nucleus of an atom is surrounded by negatively charged particles called electrons. The negative charge of an electron is equal to the positive charge of a proton, and the number of electrons in an atom is usually equal to the number of protons.

How is electricity produce?
An electric generator is a device for converting mechanical energy into electrical energy. The process is based on the relationship between magnetism and electricity. When a wire or any other electrically conductive material moves across a magnetic field, an electric current occurs in the wire. The large generators used by the electric utility industry have a stationary conductor. A magnet attached to the end of a rotating shaft is positioned inside a stationary conducting ring that is wrapped with a long, continuous piece of wire. When the magnet rotates, it induces a small electric current in each section of wire as it passes. This current is what is used for electric power.

How are electricity used?
Electricity are used in many thing including computer that we used, oven that we use to warm up food, light that help us to see better, hand phone that let us contact other ETC.

Refraction of Light by 2E1 Emily

2008-06-20T09:12:00.000-07:00

REFRACTION.
If you have ever half submerged a straight stick into water, you have probably noticed that the stick appears bent at the point it enters the water.This optical effect is due to refraction.

Refraction is the change in direction of a wave due to a change in its speed.

Refraction happens when light passes from one medium to another.
When light passes from one medium to another, light from less dense media to a denser media will slow down and it is refracted towards the normal. But when light passes from denser media to less dense media, it will speeds up and it is refracted from the normal.

REFRACTIVE INDEX
The refractive index of a medium is a measure for how much the speed of light (or other waves such as sound waves) is reduced inside the medium.

EFFECTS OF REFRACTION
refraction has some unusual effects in everyday life. some examples are :
- when you place a glass block on top of your textbook, and observe. The words will appear to be nearer to the surface of the glass than they actually are.
- the object appears to be at a higher position than it actually is. for this reason, a swimming pool appears shallower than it really is.
- a pencil inside a beaker filled with water will appear to be bent.

From all the information i have gained, i have learnt that refraction occurs in everyday life. It is very interesting to know how it happens and what are the unusual effects caused by refraction.

The Key point of this topic is : Refraction happens when light changes direction when it passes from one transparent material into another. Refraction will cause an object appears to be at higher position than it actually is.

Science Textbook Chapter 8, Refraction. http://www.ps.missouri.edu/rickspage/refract/refraction.html http://en.wikipedia.org/wiki/Refraction

Reflection of Light by 2E2 Zin Win

2008-06-20T09:10:00.000-07:00

Reflection on a mirror surface.
I have learnt that reflection is the bouncing off light after hitting a mirror surfaces.

There are two type of reflection the 1st one is regular reflection and 2nd is the diffused reflection. Regular reflection is made out of a parallel beam of light which bounce off a smooth surface and an image is form while the diffuse reflection reflects on a rough surface the ray is reflected in different direction and no image is form.

The angle of incidence is equal to the angles of reflection in the plane mirror

Properties of plane mirror:
Virtual
Upright
Same size as the object
Laterally inverted

Uses of plane mirror :
helps a driver see the traffic behind ,
help a person check appearance
make a room bigger
periscope are made of two plane mirrors to see over obstacles

Convex mirrors from upright image that is always smaller than the object. They allow many things to be seen

Concave mirrors formed upright magnified images if the object is close to the mirror. If the image is further away, the image is inverted

Electricity by 2E4 Chanchai Kovitpornsin

2008-06-20T09:08:00.000-07:00

Name class 2E4 index no. 18
Electricity
I have learnt electricity is a form of energy. It is very convenient because it be changed to other forms of energy.

How electricity produced
I have learnt electricity energy comes from 2 main sources. There are electricity and electricity cells.

Main electricity is generated in power station. The plugs of electricity appliances are inserted into mains sockets to obtain this electricity. Main electricity supplies a lot of energy.
Electricity cells give out only a little energy. They are used in many portable electrical devices and safe to use.

Electric Circuits
I have learnt to make an electrical appliance work, electricity must flow through it. The flow of electricity is called an electric current. An electric current flow only when there is: 1. A source of electrical energy and 2. A closed circuit.

Electric Current
I have learnt an electric current is the flow of electrons in one direction in a circuit.

Measuring Electric Current
I have learnt to measure the electric current, we use an ammeter.
The SI unit for electric current is the ampere (A). Smaller currents can be measured in milliamperes (mA)
1 A = 1000 mA
1 mA= 1/1000 A (or 0.001 A)

Voltage
I have learnt voltage is a measure of how much energy the electrons receive. To measure voltage we use a voltmeter.
The SI for voltage is the volt (V).

Used of electricity
Electrical energy is changed to sound energy in radios.
Electrical energy is changed to heat energy in rice cookers.
Electrical energy is changed to kinetic energy in electric fans.

Key points

Electricity is a form of energy.
Electricity energy comes from 2 main sources. There are electricity and electricity cells.

The flow of electricity is called an electric current. An electric current flow only when there is: 1. A source of electrical energy and 2. A closed circuit.
An electric current is the flow of electrons in one direction in a circuit
Voltage is a measure of how much energy the electrons receive. To measure voltage we use a voltmeter.

History
That certain objects such as rods of amber could be rubbed with cat's fur and attract light objects like feathers was known to ancient cultures around the Mediterranean. Thales of Miletos conducted a series of experiments into static electricity around 600 BC, from which he believed that friction rendered amber magnetic, in contrast to minerals such as magnetite, which needed no rubbing. Thales was incorrect in believing the attraction was due to a magnetic effect, but later science would prove a link between magnetism and electricity.

Information
http://en.wikipedia.org/wiki/Electricity
Science Discovery 2 textbook

Sound by 2E1 Shafiatul

2008-06-20T09:05:00.000-07:00

What is sound?
Sound is a vibration or a wave of air molecules which is caused by the motion of an object. The density of the molecules is higher when there is a compression wave. This compression wave travels through the air at the speed depending on the temperature of the surroundings. Since a sound wave contain energy which means it can make things move. But, if the sound wave hits something solid, the wave will bounce back forming an echo. Sound cannot travel through a vacuum. It can only travel through solids, liquids, gases and plasmas.

How is sound being produced?
Sound waves
A series of compressions and rarefactions which changes or waves through the air is called a sound wave. Sound waves vibrate at different rates or frequencies as they move through the air. Frequency is measured in cycles per second, or Hertz (Hz). The faster an object vibrates the higher the pitch of the sound. A frequency of 100 Hz means 100 vibrations every second.

Echolocation
The sound which travels to the walls and is reflected back to our ears is called an echo. Echoes are used to find objects underwater, to find large shoals of fish and to measure the depth of the sea. Animals use echoes to find food and to ‘see’ where they are going. For example, bats. They have a poor sense of sight but a good sense of hearing. They use echolocation to find food. Bats produce a high frequency sound to find insects to eat. This sound then reflects off the insect and travel back to the bat’s ears. This helps the bat to find even the smallest insect. Echolocation also helps the bat to ‘see’ where it is flying.

What affects sound?
Sound vibration
When an object moves or vibrates, sound is produced. There could be no sound without movement. When an object moves or vibrates, the air molecules around it will also vibrate. As long as they are not in a vacuum, vibrating objects produce sound. Each molecule moves back and forwards only in a tiny distance which is enough to cause the air particles to bump into each other. This will create areas where there are many molecules pushed closer. This is called compression. Areas where molecules are spread far apart are called rarefactions. Compressions and rarefactions move outwards away from the sound source in circles.

The speed of sound
Sound will take time to travel. In air, sound travels at a speed of 330 metres per second. In fresh water, sound travels at a speed of 150 metres per second. Sound travels at even higher speeds in solids. For example, an iron sound travels at 5000 metres per second. So, the speed of sound depends on density. The denser the material is the faster the speed of sound.

Examples of stuff producing sound
Here are some examples of things that produce sound:
-A guitar
-A trumpet
-A drum
-A bee (buzzing sound caused by its wings)
-A recorder
-Cars
-Airplanes
And many more.

Sources
http://www.sciencetech.technomuses.ca/english/schoolzone/Info_Sound.cfm
Explore your world with Science discovery 2 (pages 202-206)
http://en.wikipedia.org/wiki/Sound

Refraction of Light by 2E1 Lee Jae Woong

2008-06-20T09:02:00.000-07:00

Refraction
Through our project, I have learnt about refraction and its uses. Refraction refers to the bending of light as it passes between materials of different optical density.

In refraction, I learnt that the denser the material is, the slower the speed of light will be in that material. Refraction will happen when light passes from one medium to another medium with different densities.

For example, when light passes from air to a transparent glass block, the speed of light will slow down and it will cause the light ay to bend closer to the normal.

As seen in diagram 1, the light ray passes from air to a transparent glass block. The light ray, as shown, is bent towards the normal. This indicates that the speed of light is reduced when passing from one medium to another. The denser the medium is, the light ray will bend closer towards the normal. Similarly, when the light ray moves from glass block to air it is refracted away from the normal

Refractive Index
The refractive index of a medium is the measurement of how much the speed of light has reduced or increased inside various types of medium. Generally, the refractive index is subject to changes based on the incidence of the light. This explains why different colours of light travel at different speeds. The higher the index, the slower the speed of light will be through the medium.

Formula for refractive Index is n= sin i / sin r

Effects of Refraction
Effects of refraction can be seen in our everyday lives.

Firstly, refraction causes objects to appear closer than it actually is. For example, in a swimming pool, the pool looks shallower than it actually is. This is because our brains think the light has moved in a straight line. Therefore the swimming pool seems shallower than it usually is. Another example, is when we place our hand below a glass block, our hand seems nearer to the surface than it is. Thus the glass block seems thinner than the actual thickness.

As seen in diagram 2 the pool seems to be of equal depth and it looks shallow. However it is actually deeper than it looks. Due to refraction, swimming pools or ponds always appear to be shallower than they really are. When approaching air from water, the waves speed up and as a result they refract away from the normal.

Diverging rays enter the eye and the brain traces these rays back to where it thinks an image is. This results in a virtual image at a shallower depth than is the actual case.

References
1. Refraction of Light by Rick Reed http://www.ps.missouri.edu/rickspage/refract/refraction.html
2. Explore your world with Science Discovery 2 Textbook
3. Answers.Com http://www.answers.com/topic/refractive-index?cat=technology
4. http://www.asiatravel.com/turkey/istanbul/marinprincesskumburgaz/gifs/pool2.jpg
5. http://pachome2.pacific.net.sg/~ezzychan/refraction.htm

Colours of Light by 2E1 Edgar Wong

2008-06-20T09:00:00.000-07:00

How are colors produced?
Colors are produced when a light source hits a prism, which separates the white light into its separate colors are called dispersion.

How to get rainbow colors and to recombine the colors again?
Place a second prism positioned in a way that each other’s points are facing away from each other. Shine the light through both prisms.

What are primary colors?
The three primary colors are the minimum number of colors that can be mixed to make the greatest number of other colors. The primary colors cannot be made by mixing other colors.

Effects of mixing of colors.
When you mix colors together, you will get a different color. If you mix the three primary colors together, you get white.

What do you learn about that particular topic?
I’ve learn about the dispersion of white light by a prism and more about the primary colors.

Summarize the key points of that topic.
Colors, they are produced by white light hitting prisms, when lights separates its called dispersion. Placing two prisms facing away from each other can get and recombine colors. When mixing colors together, you get a different color.

Anything interesting to add?
The spectrum consists of: Red, Orange, Blue, Yellow, Green, Indigo and Violet.
Prisms separate the colors already present in the white light.

Credits.
Science Discovery, Rex M Heyworth, 128, 129 and 130, chapter 8
Color Mixing, Robert Truscio.

Colours of Light by 2E1 Marcus Choo

2008-06-20T08:58:00.000-07:00

Colour :
I have learnt that white light, ( ordinary light ), is a mixture of different colours. When a beam of white light passes through a glass prism, the light splits into seven different colours : Red, Orange, Yellow, Green, Blue, Indigo, Violet. We can get white light back again by combining the colours back together. By using a second prism, or by spinning a colour wheel.

We can see the colours of the spectrum, so it is called the visible spectrum. Some people think the there are only six colours as indigo cannot be easily distinguished from blue and violet.

There are three sections : primary colours, secondary colours and teitary colour. Primary colours consist of : Red, Blue and Green.
Secondary colours consist of : Yellow, Cyan and Magenta.
While teitary colour consist of only : White.

A colour filter is a clear plastic or glass that only lets some colours pass through and absorbs the others.

When white light shines on a colours object, some of the colours in the spectrum are reflected and some are absorbed. We see the colour of the reflected light. The colour of an object is the colour of the light that is reflected from it into our eyes.

When the eye detects light, an image is formed on the retina, ( the back of the eye ). The retina has two kinds of light sensitive cells, they are called the rods and the cones. These cells are connected to a nerve which carries signals to the brain, the brain than interprets the signals as light. The rods do not detect colour, they are sensitive to black and white, and work best in dim light. The cones however, detect colour and work best in bright light.

There are tree types of cone cells, one detects red light, another detects blue light and the other detects green light. This means that these cone cells can detect the three primary colours. When white light shines into the eye, all three types of cones respond. For example the cones which detect red light respond to the red light in the white light and the brain receives signals from all these types of cones and interprets them as white light.

Reflection of Light by 2E3 Siti Saiyidah Nafisah

2008-06-20T08:57:00.000-07:00

I have learnt that reflection is the bouncing of light off a mirror. A plane mirror is a good reflector of light.

When a ray of light strikes the mirror at a right angle, it is reflected along the same path, called the normal. When a ray of light hits a plane mirror at an angle to the normal (called the angle of incidence), it is reflected at an equal angle but on the opposite side of the normal (angle of reflection). These two angles are always equal no matter how light rays strike the mirror. These are called The Law of Reflection.

In a plane mirror, the image is upright and of the same size as the object. In a plane mirror, the image lies as far behind the mirror as the object is in front of the mirror. Mirrors turn images around from left to right. Hence, in a plane mirror, an image is laterally inverted. An image that cannot be formed on a screen is called a virtual image. In a plane mirror, the image formed is always a virtual image.

There are two types of reflection- Regular reflection and Diffuse reflection.

Textbook Resource: Science Txtbk (pg119-121)

Refraction of Light by 2E1 Jeong Seok Young

2008-06-20T08:55:00.000-07:00

In this physics holiday homework about refraction I have learnt that refraction is happening around us everyday. Example we go to our swimming pool or a bath tub and see the floors of these things are actually closer to us then it actually is.
It is also useful as we could look into fish tanks and see the fishes closer to us giving us a better view. REFER TO PICTURE BELOW
But there are disadvantages like changing the direction of the light and speed of light in different substances.

Now Im going to summarise the key points of the topic REFRACTION

-What is refraction of light?
Refraction is the bending of a wave when it enters a medium where it's speed is different.

-When does it happen? how and when will the light bend?
Refraction happens when light waves travel from a medium with a given refractive index to a medium with another. Light travels inward when entering medium of higher index of refraction.
In the other hand,light travels outward when entering medium of lower index of refraction.

-What is refractive index?
The refractive index also called index of refraction,of a medium is a measure for how much the speed of light is reduced inside the medium.

Effects of refraction?
Effects of refraction happens everyday around us. for example when we see the floors of the swimming pool, it seems closer to us but its actually further away. And when there is a straw inside the cup it should be straight but we see it as bent.

-Anything intresting to add?
What is interesting about refraction is that the lights speed of refraction differs in all different types of substances.
It is also interesting that our eyes see things closer towards us when it is not.

REFRENCES
WEBSITES:
-http://hyperphysics.phy-astr.gsu.edu/Hbase/geoopt/refr.html
-http://www.ps.missouri.edu/rickspage/refract/refraction.html
-http://sol.sci.uop.edu/~jfalward/refraction/refraction.html
-http://micro.magnet.fsu.edu/primer/java/scienceopticsu/refraction/index.html
-http://www.fishnfriends.com/pix/showtank.jpg
ALL SEARCHINGS FROM GOOGLE.COM

Colours of Light by 2E3 Nur Hasyimah

2008-06-20T08:52:00.000-07:00

I’ve learned more about colours, such as the three primary colours, the secondary colours, and lastly, the rainbow. I find that learning about rainbows is the most interesting part of this topic.

Colour is a part of the human vision system. Colours derive from the spectrum of light interacting in the eye with the spectral sensitivities of the light receptors. Dispersion of light is the separation of splitting of white light into its separate colours.

The three primary colours are red, blue, and green. Primary colours are sets of colours that can be combined to make a useful range of colours. Mixing of pigments or dyes, such as in printing, the primaries normally used are magenta, cyan and yellow. A secondary colour is a colour made by mixing two primary colours in a given colour space. For example, yellow is a secondary colour because when you mix red and green, you will get yellow.

Rainbows cause a spectrum of light to appear in the sky when the sun shines onto droplets of moisture in the earth’s atmosphere. Rainbows consist of both the primary and the secondary colours. There are seven colours in a rainbow.

There are red, orange, yellow, green, blue, indigo and violet. Rainbows can also be caused by other forms of water than rain, including mist, spray, dew, fog and ice. Rainbows can have shapes other than a bow, including stripes, circles, or even flames. Rainbows can be seen whenever there are water drops in the air and sunlight shining from behind a person on the ground. They are commonly seen near waterfalls or fountains.

Resources:
http://en.wikipedia.org/wiki/Rainbows
http://en.wikipedia.org/wiki/Primary_colours
http://en.wikipedia.org/wiki/Secondary_colours
http://en.wikipedia.org/wiki/Colours

Colours of light by 2E3 Neo Chin Yen

2008-06-20T08:50:00.000-07:00

In this topic, I get to learn the combination and recombination of rainbow colours, and how the colours are being produced, and the effects of mixing all primary colours. I also learnt that colour is a function of the human visual system, and is not an intrinsic property.

Objects don't "have" color, they give off light that "appears" to be a color. Spectral power distributions exist in the physical world, but color exists only in the mind of the beholder.

Color is the perceptual quality of light.

The color of the light coming from an object has its origin in one or more of the following processes …
emission: the object itself is a source of light with a color determined by its spectra

reflection: certain frequencies are reflected from the object while others are not

transmission: certain frequencies are transmitted through the object while others are not

interference: certain frequencies are amplified by constructive interference while others are attenuated by destructive interference

dispersion: the angular separation of a polychromatic light wave by frequency during refraction

scattering: the preferential reradiation of certain frequencies of light striking small, dispersed particles

Something interesting I want to share are some historical junks.
The painter's color wheel is a historical artifact that refuses to die. The primary colors are not red, yellow, and blue. Painters and art teachers promote this scheme. It is a convenient way to understand how to mimic one color by mixing red, yellow, and blue. But these colors do not satisfy the definition of primary colors in that they can't reproduce the widest variety of colors when combined.

Cyan, magenta, and yellow have a greater chromatic range as evidenced by their ability to produce a reasonable black. No combination of red, yellow, and blue pigments will approach black as closely as do cyan, magenta, and yellow.

The website I got all my informations are from www.hypertextbook.com/physics/

Sound by 2E1 Ebel

2008-06-20T08:48:00.000-07:00

SOUND
[A]Sound is a form of energy and is caused by objects vibrating .

[B]Sound travels through air as vibrations .When a loudspeaker produce a sound , the vibration of the skin of the speaker causes the surrounding air molecules to also vibrate . These vibration spread outwards , passing on the sound energy until it reaches the ears.

[C]Sound takes time to travel from one place to the other. Sound travels at a speed of 330m/s in air .This is much slower than the speed of light [300 000 000m/s]Thats why you will always see the flash of lighting followed by the crack of thunder .

[D]Sound cannot travel through a vacuum[empty space] it needs a medium[substance] to travel through .Sound can travel through gases , liquid and solids. It travels through liquid and solids faster than gases as the particles of solid and liquids are closer , so the vibration pass more easily .However , the energy of the sound is soon used up passing through liquids and solids .

[E]Sound are all around us and provide a means of communication [talking , whistling and singing ] give us warning signals [alarms , telephones , fire bells , police sirens] give us pleasure [music , singing ]

[F]However some sound are unnecessary , they are describes as noise [ traffic noise , loud music , aircraft noise , building sites noise , drilling noise ]. Sound levels are measured as decibels[dB].The loudest sound , which causes pain is called the threshold of pain.

[G]The ear is the natural detector of sound . The external ear is like a funnel to channel the sound waves towards the ear drum .This then starts to vibrate and the bones in the middle ear amplify this vibration which causes waves in the liquid inside the inner ear. These waves produce electrical pulses in the nerve cells which are carried by the auditory nerve to the brain intercepts these electrical signs as sounds

Biobliography:Science Keynotes -Christopher N. Prescott

Refraction of Light by 2E4 Sudha

2008-06-20T08:46:00.000-07:00

I learnt : when the light moves from air to glass,it is refracted towards the normal & when the light moves from glass to air,it is refracted away from the normal.

And also that light from an object bends as it comes out of water ; but our brain thinks the light has moved in a straight line. So, the object appears to be at a higher position than it actually is.

the key points :
Light is bent or refracted when it passes from one transparent material into another,such as from air to glass and vice versa.

Two effects of refraction are (a)an object in water appears nearer to the surface than it really is and (b)an object such as a stick placed in water appears to be bent.

Refraction is the change in direction of a wave due to a change in its speed. This is most commonly seen when a wave passes from one medium to another.
In optics, refraction occurs when light waves travel from a medium with a given refractive index to a medium with another. At the boundary between the media, the wave's phase velocity is altered, it changes direction, and its wavelength increases or decreases but its frequency remains constant.

For example, a light ray will refract as it enters and leaves glass; understanding of this concept led to the invention of lenses and the refracting telescope.

Refraction of Light by 2E4 Shamani Rachel

2008-06-20T08:45:00.000-07:00

I learnt from this particular topic that,when the light moves from air to glass,it is refracted towards the normal & when the light moves from glass to air,it is refracted away from the normal.

And also that light from an object bends as it comes out of water ; but our brain thinks the light has moved in a straight line. So, the object appears to be at a higher position than it actually is.

& to summarise the key points :
Light is bent or refracted when it passes from one transparent material into another,such as from air to glass and vice versa.

Two effects of refraction are (a)an object in water appears nearer to the surface than it really is and (b)an object such as a stick placed in water appears to be bent.

Refraction is responsible for image formation by lenses and the eye.
The Snell's Law :D
In 1621, a Dutch physicist named Willebrord Snell (1591-1626), derived the relationship between the different angles of light as it passes from one transperent medium to another.

When light passes from one transparent medium to another, it bends according to Snell's law which states:
Ni * Sin(Ai) = Nr * Sin(Ar),

where: Ni is the refractive index of the medium the light is leaving, Ai is the incident angle between the light ray and the normal to the meduim to medium interface, Nr is the refractive index of the medium the light is entering, Ar is the refractive angle between the light ray and the normal to the meduim to medium interface.

*Information taken from,
www.google.com.sg :
http://www.ps.missouri.edu/rickspage/refract/refraction.html
http://hyperphysics.phy-astr.gsu.edu/Hbase/geoopt/refr.html
& the science textbook.

Sound by 2E4 Luan Niannian

2008-06-20T08:42:00.000-07:00

What is sound?
Soundis a from of energy.It is caused by vibrations.Sound is the quickly varying pressure wave within a medium. We usually mean audible sound, which is the sensation (as detected by the ear) of very small rapid changes in the air pressure above and below a static value. This "static" value is atmospheric pressure (about 100,000 Pascals) which does nevertheless vary slowly, as shown on a barometer. Associated with the sound pressure wave is a flow of energy.

Sound is often represented diagrammatically as a sine wave, but physically sound (in air) is a longitudinal wave where the wave motion is in the direction of the movement of energy. The wave crests can be considered as the pressure maxima whilst the troughs represent the pressure minima.

How small and rapid are the changes of air pressure which cause sound?

When the rapid variations in pressure occur between about 20 and 20,000 times per second (i.e. at a frequency between 20Hz and 20kHz) sound is potentially audible even though the pressure variation can sometimes be as low as only a few tens of millionths of a Pascal. Movements of the ear drum as small as the diameter of a hydrogen atom can be audible!

Louder sounds are caused by greater variation in pressure. A sound wave of one Pascal amplitude, for example, will sound quite loud, provided that most of the acoustic energy is in the mid-frequencies (1kHz - 4kHz) where the human ear is most sensitive. It is commonly accepted that the threshold of human hearing for a 1 kHz sound wave is about 20 micro-Pascals.

What makes sound?
Sound is produced when the air is disturbed in some way, for example by a vibrating object. A speaker cone from a high fidelity system serves as a good illustration. It may be possible to see the movement of a bass speaker cone, providing it is producing very low frequency sound. As the cone moves forward the air immediately in front is compressed causing a slight increase in air pressure, it then moves back past its rest position and causes a reduction in the air pressure (rarefaction). The process continues so that a wave of alternating high and low pressure is radiated away from the speaker cone at the speed of sound.

What affects sound?
Sound can travel through solids,liquids and gases.Sound cannot travel through vacuum because it requires a medium to travel. Voices in different substances in different speed. The speed of sound effects spread to two factors: media and wave source The surrounding temperature changes, the density of the air has changed (the higher the temperature, density greater, because the higher the temperature, air Lengsu heat up, so will have partial pressure increases, that is, increasing density) is the medium change The The voice of the spread of medium density greater voice transmission of the greater speed That is, the higher the temperature in the voice of the environment in the faster spread

What is a decibel (dB)?
The decibel is a logarithmic unit which is used in a number of scientific disciplines. Other examples are the Richter scale for earthquake event energy and pH for hydrogen ion concentration in liquids.
In all cases the logarithmic measure is used to compare the quantity of interest with a reference value, often the smallest likely value of the quantity. Sometimes it can be an approximate average value.
In acoustics the decibel is most often used to compare sound pressure, in air, with a reference pressure. References for sound intensity, sound power and sound pressure in water are amongst others which are also commonly in use.

How is sound measured?
A sound level meter is the principal instrument for general noise measurement. The indication on a sound level meter (aside from weighting considerations) indicates the sound pressure, p, as a level referenced to 0.00002 Pa, calibrated on a decibel scale.

http://www.tek-ltd.com/school2.htm

Electricity by 2E1 Chen Meng

2008-06-20T08:37:00.000-07:00

What is electricity?
It is a controllable and convenient form of energy,
evident from the fact that it runs machinery and can
be transformed into other types of energy such as
light and heat.

It is invisible. During an electrical
storm, we do not see electricity.
We observe the air being ionized when
the electricity travels through it.

Sources of electricity
Electrical energy comes from two main sources. There are mains electricity and electric cells.

Main electricity is generated in power stations. The plugs of electrical appliances are inserted into mains sockets to obtain this electricity. Mains electricity supplies a lot of energy. It can give us an electric shock which can kill us. Never touch bare wires connected to mains electricity.
Electric cells give out only a little energy. They are used in many portable electrical devices and are safe to use.

Types of electricity
Static electricity is electricity that says still on objects.
Current electricity is electricity that flows in an electric circuit.

Electric circuits
To make an electrical appliance work, electricity must flow through it. The flow of electricity is called an electric current.
The path along which the electric current moves is called the electric circuit.

In the laboratory, experiments with electricity are often done on a circuit board.
On the circuit board, we join up electrical components to make a circuit.

Closed circuit & open circuits
For the bulb to light up, there has to be a complete path without any gap from one end of the cell to the light bulb and back to the other end of the cell. This complete path is called a closed circuit.
Each circuit has a gap in it and the bulbs do not light up. Incomplete circuits are called open circuits.
An electric current flow only when there is a source of electrical energy and a closed circuit.

Cell
Supplies electrical energy.The larger terminal (on the left) is positive (+). A single cell is often called a battery, but strictly a battery is two or more cells joined together.

Battery
Supplies electrical energy. A battery is more than one cell.The larger terminal (on the left) is positive (+).

Output Devices: Lamps, Heater, Motor, etc.

Component
Circuit Symbol
Function of Component

Lamp (lighting)
A transducer which converts electrical energy to light. This symbol is used for a lamp providing illumination, for example a car headlamp or torch bulb.

Lamp (indicator)
A transducer which converts electrical energy to light. This symbol is used for a lamp which is an indicator.

Heater
A transducer which converts electrical energy to heat.

Motor
A transducer which converts electrical energy to kinetic energy (motion).

Bell
A transducer which converts electrical energy to sound.

Buzzer
A transducer which converts electrical energy to sound.

Push Switch(push-to-make)
A push switch allows current to flow only when the button is pressed. This is the switch used to operate a doorbell.

Push-to-Break Switch
This type of push switch is normally closed (on), it is open (off) only when the button is pressed.

On-Off Switch(SPST)
SPST = Single Pole, Single Throw.An on-off switch allows current to flow only when it is in the closed (on) position.

Resistor
A resistor restricts the flow of current, for example to limit the current passing through an LED. A resistor is used with a capacitor in a timing circuit. Some publications still use the old resistor symbol:

Variable Resistor(Rheostat)
This type of variable resistor with 2 contacts (a rheostat) is usually used to control current. Examples include: adjusting lamp brightness, adjusting motor speed, and adjusting the rate of flow of charge into a capacitor in a timing circuit.

Voltmeter
A voltmeter is used to measure voltage. The proper name for voltage is 'potential difference', but most people prefer to say voltage!

Ammeter
An ammeter is used to measure current.

Ohmmeter
An ohmmeter is used to measure resistance. Most multimeters have an ohmmeter setting.

Switches
A switch is used to open or close a circuit.

Conductors & Insulators
Allows electricity to pass through it is called an electrical conductor.
A material which does not allow electricity to pass through it is called an electrical insulator.

What is voltage?
Voltage is a measure of how much energy the electrons receive. To measure voltage we use a voltmeter.
The SI unit for voltage is the volt (V).

Series circuits & parallel circuits
Electric circuits can be classified into two main types----series circuits and parallel circuits.

In a series circuits, each component is joined to the next to form a single path. The current that flows through each of the components is the same. However, a break in any part of a series circuit stops the flow of current in the whole circuit.
☆ the current at different points of the electric circuit is the same.
☆ the voltage of the energy source is the sum of the voltage of all the batteries in series.
☆ the total voltage across the whole circuit is the sum of the voltage of all the batteries in series.

A parallel circuit divides into two or more branches with electrical components in each branch. The current divides and flows through each of the three branches. An advantage of this circuit is that if one bulb breaks or is removed, the other bulbs remain lit.
☆ the current is the sum of all the current in the braches of a parallel circuit.
☆ the voltage across each branch is the same.
☆ the total voltage of cells/batteries connected on parallel is the voltage of one cell/battery.

What is an Electric Current?
An electric current is the flow of electrons in one direction in a circuit.

How does electricity travel in circuits?
Electricity travels in closed circuits. It must have a complete path before the electrons can move. If a circuit is open, the electrons cannot flow. When we flip on a light switch, we close a circuit. The electricity flows from the electric wire through the light and back into the wire. When we flip the switch off, we open the circuit. No electricity flows to the light. Electricity flows through a tiny wire in the bulb when we turn a light switch on. The wire gets very hot. It makes the gas in the bulb glow. When the bulb burns out, the tiny wire has broken. The path through the bulb is gone.

Measuring electric current
An ammeter is used to measure the electric current.

The SI unit for electric current is the ampere (A). Smaller currents can be measured in milliamperes (mA)
1A=1000mA
1mA=1/1000A

What is resistor?
An electricity component that is specially made to have a certain resistance is called a resistor.
Resistors that have one fixed resistance are called fixed resistors.

We used rheostat to change the current in a circuit. (rheostat which is also called a variable resistor.)
Resistance = voltage across component /
Current though component

Effects of an electric current
The flow of an electric current produces three effects.
☆ HEATING effect
☆ CHEMICAL effect
☆ MAGNETIC effect

The above sources are taken from website and sec. 2 textbook.
http://www.eia.doe.gov/kids/energyfacts/sources/electricity.html
http://www.sciencetech.technomuses.ca/english/schoolzone/Info_Electricity.cfm#whatis
http://people.virginia.edu/~bwk7j/basic.htm
http://www.kpsec.freeuk.com/symbol.htm

Reflection of Light by 2E3 Elson Yeo

2008-06-20T00:58:00.000-07:00

What is reflection of light?
When you look into a mirror, you see a picture of yourself. What you see is called an image. The image in a mirror is formed when light rays bounce off the mirror and travel to your eyes. This bouncing of light off a mirror is called reflection.

A flat mirror, called a plane mirror, is a good reflector of light. When a ray of light strikes the mirror at a right angle, it is reflected along the same path.

Scientists call this line the normal. When a ray of light hits a plane mirror at an angel to the normal, called the angel of incidence, it is reflected at an equal angle but on the opposite side of the normal, the angel of reflection. These two opposite side of the normal, the angle of reflection. The two angels are always equal no matter how light rays strike the mirror.
This generalization is called the law of reflection.

When does it happen?
When a ray of light hits a surface, it bounces off or reflects and then reaches our eyes. This phenomenon by which a ray of light changes the direction of propagation when it strikes a boundary between different media through which it cannot pass is described as the reflection of light

Types of reflection
There are two types of reflection – regular reflection and diffuse reflection.
When a parallel beam of light hits a smooth surface such as a plane mirror, it is reflected as a parallel beam. This is called regular reflection. An image is formed with regular reflection. That is, when we look at a smooth surface, we can see an image.

Most surfaces are actually quite rough. When a beam of light hits a rough surface, the individual rays are reflected in different directions. So no image is formed. This type of reflection is called diffuse reflection.

Uses of reflection of light and examples?
Convex mirrors are often used in shops as security mirrors because of the type of image produced by that mirror. The image is smaller but shows a wide angle view of the shop.
Concave mirrors are often used in torch lights or in the headlights of cars. The light travels in all directions from the light globe towards the mirror behind it. The rays are then reflected by the mirror and they form a beam of light (a bundle of parallel rays).

http://www.tutorvista.com/content/science/science-ii/reflection-light/reflection-light.php
http://www1.curriculum.edu.au/sciencepd/readings/ligh_reflection.htm
Textbook Page 119 , 121 & 122

Electricity by 2E3 Joevenn Ng

2008-06-20T00:56:00.000-07:00

What Is Electricity?
Electricity is the flow of electrical power or charge. It is a secondary energy source which means that we get it from the conversion of other sources of energy, like coal, natural gas, oil, nuclear power and other natural sources, which are called primary sources. The energy sources we use to make electricity can be renewable or non-renewable, but electricity itself is neither renewable or non-renewable.
Source for this question: http://www.eia.doe.gov/kids/energyfacts/sources/electricity.html

How Is Electricity Produced?
Electricity generation - whether from fossil fuels, nuclear, renewable fuels, or other sources - is usually* based on the fact that "When magnets are moved near a wire, an electric current is generated in that wire."
"When magnets are moved near a wire, an electric current is generated in that wire."
Source for this question: http://hawaii.gov/dbedt/info/energy/renewable/electricitygeneration/

Uses Of Electricity.
Well electricity is widely used all around the world. They are used to do things like using a computer , charging of handphones and others. Electricity is used or all used for good and bad things.

Reflection of Light by 2E2 Andre Lim

2008-06-20T00:55:00.000-07:00

Topic: Reflection of light – i. What is reflection of light?
ii. When does it happen?
iii. Types of reflection
iv. Uses of reflection of light, examples?

Reflection is the bouncing of light off a mirror or mirror-like surface. Reflection is also the change in direction of a wave front at an interface between two different media so that the wave front returns into the medium from which it originated from.
A flat mirror called a plane mirror is a good reflector of light. A normal is formed when a ray of light strikes the mirror at a right angle.

-Reflection may even occur on water and clouds
Mainly, there are two types of reflection, specular and diffused.Light being reflected of a smooth surface is Specular. When light strikes this smooth surface, all the reflected rays are in line with each other. An image is formed.

Diffused reflection is reflection from a rough surface. The small bumps and irregularities on a rough surface will cause each of the light rays to reflect n different directions, thus no image is formed.

There are some uses of plane mirrors, for example, plane mirrors helps people to check their appearance, and see things at a certain angle which the eye cannot.

The use of curved mirrors is used to reflect light into microscope to amplify the image’s size and dentist can use it to magnify the image of a patient’s teeth.

Also, if you look place a screen behind the mirror, the image is not formed on the screen. An image that cannot be formed on a screen is known as a virtual image.

Acknowledgement: http://en.wikipedia.org/wiki/Reflection_(physics)#Laws_of_regular_reflection
Sec 2 Science Text Book
Pictures - http://en.wikipedia.org/wiki/Image:Crepuscular_Rays_in_ggp_14.jpg

Electricity by 2E2 Amruth

2008-06-20T00:53:00.000-07:00

What is electricity?
*Electricity is a form of energy and it is convenient as it can be changed into other forms of energy.

What are the effects of electricity on our daily lives?
*We are able to; play games on our computer, travel in cars and other transportations, Watch television, use handphones, etc.

What is the electric current?
*It is the flow of electricity.

What is the electrical circuit?
*It is the path where current moves.

What is the meaning of closed circuit and open circuits?
Closed circuit

*It is a complete path of electricity from one end to the other.
Open circuit

*It is an incomplete path of electricity from one end.
Why are switches used in our daily life?
It is safer way to conduct electricity and to open and close circuits.

What is voltage?
*Voltage is the energy per unit charge.

What is the SI unit for voltage?
*The SI unit for voltage is volt ( V ).

Some interesting stuff…….
*In the times when humans first appeared on Earth, the created electricity by rubbing two materials together.
*The first machine to make an electrical spark was created at 1650; it worked by rubbing a hand on a spinning sulphur ball…. Electricity through friction?

RESOURCES
http://www.historyoftheuniverse.com/electric.html
http://en.wikipedia.org/wiki/Voltage
Book: Explore your world with SCIENCE DISCOVERY 2
Publisher: Pearson Longman
Author : Rex M Heyworth

Electricity by 2E2 Naqiah

2008-06-20T00:49:00.000-07:00

Electricity
Electricity is a form of energy produced by the movement of electrons. Electricity is electrical power or an electric current. This form of energy can be sent through wires in a flow of tiny particles. It is used to produce light and heat and to run motors.

Electricity is a basic feature of all matter, of everything in the universe. Electrical force holds atoms and molecules together. Electricity determines the structure of every object that exists. Together with magnetism, it causes a force called electromagnetism, a fundamental force of the universe. Electricity or electrical signals are essential to many biological processes. In our bodies, electrical signals are carried through the nervous system, moving information to and from the brain. Electrical signals communicate to our brain what the eyes see, what the ears hear, and what the fingers feel.

Electrical signals from our brain causes our muscle movements. Electrical signals cause each heartbeat. One of the most important forms of electricity is in electrical current. During the industrial revolution of the 1800s, people began to find ways to use electricity to do work. Today electricity is used throughout our homes, at work, in communication, in transportation, and in medicine and science.

Electrically powered devices are prevalent. Relatively cheap electricity has made electrical appliances, machines, and other devices possible. A major reason electricity works is because of conductors. First metal, water, tall trees and tall items are good conductors because lightning is attracted to them. These materials have many mobile electrons.

Metal is an easy substance for lightning to travel through so metals are good conductors.However, rubber is a bad conductor because lightning bounces off of it. A bad conductor is called an insulator. An insulator has a few mobile electrons. It is important for us to know the difference between good conductors and insulators because if you're outside in an open field during a storm you will know where to go to be safe from the lightning. Truly, knowing the difference between conductors and insulators of electricity can save our lives.

It is a secondary energy source which means that we get it from the conversion of other sources of energy, like coal, natural gas, oil, nuclear power and other natural sources, which are called primary sources. The energy sources we use to make electricity can be renewable or non-renewable, but electricity itself is neither renewable or non-renewable.

(http://library.thinkquest.org/J001647F/)(http://42explore.com/electric.htm)

Sound by 2E1 Tan Hui Yu

2008-06-20T00:48:00.001-07:00

What is sound?
Sound is a mechanical wave which results from the back and forth vibration of the particles of the medium through which the sound wave is moving. If a sound wave is moving from left to right through air, then particles of air will be displaced both rightward and leftward as the energy of the sound wave passes through it. The motions of the particles are parallel (and anti-parallel) to the direction of the energy transport. This is what characterizes sound waves in air as longitudinal waves.

How is sound being produced?
Sound are produced by the vibration of object . Sound is a physical entity, unlike noise which is the perception of sound. Sound is an high pressure wave front through a medium (such as air, or a liquid such as water, or a solid), wherein the wave front is followed by a reciprocal pressure differential behind it. Sound is produced when something disturbs the medium and sets in motion the molecules in the medium.

What affects sound?
One thing that can propagate sound is if you were to place something of which emits sound in a vacuum. The sound waves will propagate in the vacuum, because the matter which supports the sound called the medium no longer exists.
Source, http://en.wikipedia.org/wiki/Sound

Examples of stuff producing sound .
There are many things that can produce sound
Examples are radios , television , printers , fans .

What did I learn about the particular topic ?
I learn that sound is part of our life as it is everywhere . When we cough , a sound is made . When we talk or laugh with our friends , a sound is made . So it is very common to have sound everywhere .

Key points of the topic
Sound is a form of energy .
Are produced by the vibration of objects .
Sound travels through matter-solids, liquids and gases . Sound cannot travel through a vacuum .

Sources : Textbook resource , Source, http://en.wikipedia.org/wiki/Sound

Reflection of Light by 2E3 Ying jie

2008-06-20T00:44:00.000-07:00

The bouncing of light off a mirror is called reflection.
Law of reflection
The ray of light approaching the mirror is known as the incident ray .The ray of light which leaves the mirror is known as the reflected ray .
At the point of incidence where the ray strikes the mirror, a line can be drawn perpendicular to the surface of the mirror, and this is called normal line.
The angle between the incident ray and the normal is known as the angle of incidence.
The angle between the reflected ray and the normal is known as the angle of reflection.
The law of reflection states that when a ray of light reflects off a surface THE ANGLE OF INCIDENCE = ANGLE OF REFLECTION .
Another law of reflection ,is Light travels in straight lines.

In a plane mirror ,
1. Image is Upright and of the same size of the object
2. Images lies as far behind the mirror as the object is in front of the mirror .
3. Image is laterally inverted .
4. image is always virtual image .
An image that cannot be formed on a screen is called VIRTUAL IMAGE.

Uses of the plane mirror,
Helps the driver to see the traffic behind , Makes room look bigger , Check their appearance .

Two types of reflection ,
Regular reflection – When a parallel beam of light hits a smooth surface , it is reflected as a parallel beam . An image is formed.

Diffuse reflection – When a beam of light hits the rough surface , individual rays are reflected in different directions. No image is formed .

Uses Of Curved mirrors ,

Convex Mirrors- Is a fish eye mirror or diverging mirror, is a curved mirror in which the reflective surface bulges toward the light source.
Upright images that are smaller than object. By the same time it allows many things to be seen.

Uses of Convex Mirrors :
1.Camera phones use convex mirrors to allow the user correctly aim the camera while taking a self-portrait.
2.The passenger-side mirror on a car is typically a convex mirror. It gives a safety warning "Objects in mirror are closer than they appear", to warn the driver of the convex mirror's distorting effects on distance perception.

Concave mirrors – Upright magnified images if the object is close to the mirror . If it is further away , the image is inverted .

Uses of Concave Mirrors :
Dentist mirror magnifies the image of our teeth .
Used to reflect light into microscope.

Colours of Light by 2E2 Riesky

2008-06-20T00:41:00.000-07:00

The colors are being produced when light passes through a prism and dispersion is the separation or splitting of white light into its separate colors.

The most famous example of dispersion is a rainbow, in which dispersion causes the spatial separation of a white light into components of different colors. However, dispersion is the most often explained for light waves, but it possibly occur for any kind of wave that interacts with a medium or passes through an inhomogeneous geometry. On the other hand dispersion also has an impact in my other circumstances.

Ordinary light (white light )is really a mixture of different colors. When a beam of white light passes through a glass prism, the light splits up into the colors you see is a rainbow. These colors are called the spectrum of white light.

The spectrum consists of seven colors: Red, Orange, Yellow, Green, Blue, Indigo and Violet or You can remember the order of the seven colors as a boy’s name: ROY G BIV. As these colors merge one into another gradually, it is difficult to say exactly where one colors ends and the next colors starts.

A rainbow is formed when sunlight (white light) passes through raindrops. These drops of water act as small prisms. The white light separates to form the colors of the spectrum.

Since white light consists of seven colors, we should be able to get white light again by combining the colors together. There are 2 ways:
By using a second prism
Spinning a color wheel
White light and light of other colors can be obtained by mixing just three colors – red, blue and green.

These colors are called the primary colors of light.

There are 2 basic ways colors can be mixed to make other colors. One is by combining color light. Mixing color light is called additive color mixing, because the combined colors are formed by the adding of light from 2 or more light sources together. Two or more lights added together will give more illumination than any of the lights by them selves.
If colored light is mixed together, the brightness of the colored lights are added together. This can be seen where the color illumination overlaps. The yellow mixed from red plus green will be brighter than either the red light or green light alone.

Likewise the color cyan is formed by adding green light and blue light. The cyan is also brighter than its two components.
green light + blue light = cyan
The same goes for the magenta and its mixture of red and blue.
red light + blue light = magenta
White light is formed where all three additive primary colors overlap. Since the white mixture results from the adding of all three color light sources, the white light mixture appears even brighter yet.

PRIMARY COLORS OF LIGHT
By varying the amount of the individual light sources, a full range of colors can be obtained. Television screens and PC monitors use the additive color process.

(http://en.wikipedia.org/wiki/Dispersion_(optics)
(http://home.att.net/~RTRUSCIO/COLORMX.htm)
Text book pg (128, 129 and 130)

Reflection of Light by 2E3 Li Yanbing

2008-06-20T00:39:00.000-07:00

1) WHAT IS REFLECTION OF LIGHT?
The bouncing of light off a mirror is called reflection.

2) WHEN DOES IT HAPPEN?
Reflection happen when the image in a mirror is formed when light rays bounce off the mirror and travel to your eyes.

3) TYPES OF REFLECTION

There are basically two types of reflection:

Regular Reflection
When a parallel beam of light hits a smooth surface such as a plane mirror, it is reflected as a parallel beam. This is called a REGULAR reflection.That is when we look at a smooth surface,we see an image.

Diffuse Reflection
When a beam of light hits a rough surface, the individual rays are reflected in different direction. So no image is formed. This type of reflection is called DIFFUSE reflection.

4) USE OF REFLECTION OF LIGHT; EXAMPLES.
There are many examples of the use of reflection of light.
The rear view mirror of a car helps drivers to see traffic behind the car.
The use of plane mirrors to check one’s appearance.
Periscopes are made of two plane mirrors which see over obstacles such as walls.
Mirrors used in double-deck buses to help the driver to see the passengers on the upper deck.

Sources:
Heyworth, Rex M. Explore Your World with Science Discovery 2.
Diagram obtained from <http://www.rebeccapaton.net/rainbows/rflctn.gif>

Colours of light by 2E2 Liow Fang Yu

2008-06-20T00:38:00.000-07:00

Colours of light
I learnt that sunlight may appear white, but it is actually made up of a mixture of seven colours. When the sunlight passes through the rain drop, the raindrop split the white sunlight into a range or spectrum of colours. The colours that makes the spectrum are red, orange, yellow, green, blue, indigo and violet.

We can see the colours of the spectrum, so it is called the visible spectrum . I learnt that I can also remember the order of the seven colours as a boy’s name: ROY G BIV

I learnt that when the splitting or separation of whit light into a spectrum of colours is called the dispersion of white light.

As the refracted colours of light leave the prism, they are bent again, but not in their original paths. This is because the face of the prism through which the light leaves is not parallel to the face through which it enters.

I learnt that to prove that white light is a mixture of different colours, another prism can be used to recombine the colours of its spectrum. Another way of combining the different colours of a spectrum is by spinning a rainbow-coloured disc called Newton’s disc.

I learnt that when a white light is a mixture of different colours, another prism can be used to recombine the colours of its spectrum. I learnt that white light and light of other colours can be obtained by lust mixing three colours. These three colours are red, blue and green. These three colours are called the primary colours of light.

Mixing the primary colours two at a time gives the following colours:
RED + BLUE = MAGENTA
RED + GREEN = YELLOW
BLUE + GREEN = CYAN

A colour television works in the same way. The picture on the television screen is made of dots of coloured light. A mixture of red, green and blue dots in different combinations and varying amounts of brightness produces the different colours in the picture.

These information can be found in : Interactive Science 2 (book) pg113 to119 and
Explore your world with science discovery 2 (book) pg128 to 130.

Electricity by 2E2 Siti Azwani

2008-06-20T00:35:00.000-07:00

Electricity
i) I have learnt that electricity is a controllable and convenient form of energy used in everyday life. Electricity is the flow of electrons. Without it, we may not be able to perform our everyday routine. Mainly, we used electricity for work, play, in the house and at work, (and at school).

ii) Electricity is a basic part of nature and it is one of our most widely used forms of energy. We get electricity, which is a secondary energy source, from the conversion of other sources of energy, like coal, natural gas, oil, nuclear power and other natural sources, which are called primary sources.

In every electricity, there will always be an electric current. An electric current is a flow of electric charge around a circuit. The charge is already in the wires. This charge is evenly spread out through the wires. As soon as you close the switch, the cell starts to push on the charge. So all the charge starts moving at once. An electric cell gives energy to the electrons and pushes them around a circuit.

Voltage is a measure of how much energy the electrons receive.

iv) acknowledge from: sec 2 Science textbook and wikipedia.com

Reflection of Light by 2E4 Gao YanTing

2008-06-20T00:33:00.001-07:00

Reflection is the bouncing of light off an object,when light falls on the object.

The laws of reflection :

The angle of incidence is equal to the angle of reflection.

The incident ray , the reflected ray and the normal at the point of incidence all lie on the same plane.

There are two types of reflection :

Regular reflection ---- a parallel beam of light is reflected as a parallel beam in the same direction to form clear images,occurs on smooth surfaces.

Diffused reflection ----- a parallel beam of light is reflected in different directions without forming any image,occurs on rough surfaces.

Uses of Plane Mirror

Help the driver to see traffic behind

Make a room look bigger

Check their appearance

Uses of Curved Mirrors

Convex --- Security mirrors are used in shops

Blind corner mirrors help drivers to see objects around the corner

Concave ---- Aconcave mirror is used to reflect light into the microscope

A dentist's mirror magnifies the image of your teeth.

From:Git it right
and Text book

Reflection of Light by 2E4 Ding Ruxin

2008-06-20T00:31:00.000-07:00

1.Reflection of light is very predictable. The Law of Reflection describes it simply as "The angle of incidence is equal to the angle of reflection."

2.Law of reflection: ' = where is the angle of incidence and ' is the reflected angle from the normal.

Yeah, that is great for flat surfaces but what about curved surfaces? It works the same way. Simply draw the tangent line to the point of the curve and reflect the light according to the tangent line.
There are actually two types of reflections: specular and diffused.
Specular reflection is reflection from a smooth surface. When light strikes this smooth surface, all the reflected rays are in line with each other.

Diffused reflection is reflection from a rough surface. The small bumps and irregularities on a rough surface will cause each of the light rays to reflect in different directions, all following the law of reflection of course.

Any incident ray traveling parallel to the principal axis on the way to a concave mirror will pass through the focal point upon reflection.
Any incident ray passing through the focal point on the way to a concave mirror will travel parallel to the principal axis upon reflection.

3 .Materials that reflect neutrons, for example beryllium, are used in nuclear reactors and nuclear weapons. In the physical and biological sciences, the reflection of neutrons off atoms within a material is commonly used to determine its internal structures.

4. http://library.thinkquest.org/27356/p_reflection.htm

Reflection of Light by 2E4 Zhang Ling

2008-06-20T00:30:00.000-07:00

What is reflection?
1．Reflection is the change in direction of a wave front at an interface between two different media so that the wave front returns into the medium from which it originated. Common examples include the reflection of light, sound and water waves.
Reflection of light may be specular (that is, mirror-like) or diffuse (that is, not retaining the image, only the energy) depending on the nature of the interface. Furthermore, if the interface is between dielectric-conductor or dielectric-dielectric media, the phase of the reflected wave may or may not be inverted, respectively.

2．（1）Reflection of light
In the diagram, a light ray PO strikes a vertical mirror at point O, and the reflected ray is OQ. By projecting an imaginary line through point O perpendicular to the mirror, known as the normal, we can measure the angle of incidence, θi and the angle of reflection, θr. The law of reflection states that θi = θr, or in other words, the angle of incidence equals the angle of reflection.
In fact, reflection of light may occur whenever light travels from a medium of a given refractive index into a medium with a different refractive index.

（2）Laws of regular reflection
If the reflecting surface is very smooth, the reflection of light that occurs is called specular or regular reflection. The laws of reflection are as follows:
The incident ray, the reflected ray and the normal to the reflection surface at the point of the incidence lie in the same plane.
The angle which the incident ray makes with the normal is equal to the angle which the reflected ray makes to the same normal.
（3）Diffuse reflection
When light strikes a rough or granular surface, it bounces off in all directions due to the microscopic irregularities of the interface. Thus, an 'image' is not formed. This is called diffuse reflection.

3．Light bounces exactly back in the direction from which it came due to a nonlinear optical process. In this type of reflection, not only the direction of the light is reversed, but the actual wavefronts are reversed as well. A conjugate reflector can be used to remove aberrations from a beam by reflecting it and then passing the reflection through the aberrating optics a second time.

4．http://en.wikipedia.org/wiki/Reflection_%28physics%29#Reflections

Sound by 2E1 Desiree Ang

2008-06-20T00:27:00.000-07:00

What is sound?
CRASH BANG! Did you hear that sound? This is called sound and you hear sound everyday. Sound is a form of energy and they are produced by the vibration of objects and the number to count vibration/sec is frequency. Frequency is measured in hertz (Hz).

Transmission of sound.
Sound travels through solid, liquids and gases in 330m/s from one place to another. However, sound cannot travel through a vacuum. Sound travels in a form of waves.

Pitch and music.
A musical note is called a tone which is produced by air vibrating a certain number of times per second. Some instruments have a string, reed or some other devices to create sound waves when moved. A high pitch has high frequency while a low pitch has low frequency. For wind instruments, the shorter the column of air, the higher the pitch of a note.

Natural sound producer.
Our vocal cords are our natural sound producer.

The human ear.
It is a sound detector and it has 3 main parts. The outer ear, middle ear and inner ear. The human ear can only hear a limited range of sound frequencies.

The importance of sound
Sound is a form of communication and warning signal. So it is important. However, noise that is loud, is unpleasant. Sounds above 90dB can cause damage to our ears and if you want to reduce noise level, ear protectors are used. Sound frequencies that are higher than those detected by humans, are used as ultrasound used in the medicinal industry.
A world without sound can cause one to be lonely and lost. Hence, sound is important!

Credits`: http://library.thinkquest.org/5116/sound.htm and science discovery 2 (textbook)

Colours of Light by 2E3 Mageshwary

2008-06-20T00:25:00.001-07:00

In this topic I learned about colours, what causes the colours in a rainbow, what is a spectrum, what is called dispersion, what are the seven main colours of the visible spectrum, what are the primary colours and the mixing of colours.

The key points of this topic are, a spectrum is a band of colours. The rainbow is a spectrum of white (ordinary) light into its component colours, white light can be dispersed using a prism, the spectrum of white light consist of seven colours: red, orange, yellow, green, blue, indigo, and violet,

The colours of the spectrum can be recombined to give white light, rainbows are formed by the dispersion of white light by raindrops,

red, green and blue are the primary colours of light, white light can be combined by mixing red, green and blue lights, a colour filter is clear plastic or glass that lets through some colours but absorbs the others, a red filter allows red light to pass through, an object has an certain colour because it reflects light of that colour and absorbs light of other colours.

The interesting things are that a prism can be used to break apart white light into its component colours. This shows that white light is a mixture of the projected colours.

Although the spectrum shows that white light contains a continuous rage of colours, colours from just three areas of the spectrum could be mixed to form any other colour including white. These three colours of light are from the red, green and blue parts of the spectrum. When the three primary colours of light is being added. This can be seen where the primary colour illumination over laps. The yellow formed when red light is added to green light is equal to the illumination of the red and green combined.

This information is taken from the school science text book and,http://home.att.net/~B-P.TRUSIO/COLOR.htm

Reflection of Light by 2E2 Elizabeth Lee

2008-06-20T00:23:00.000-07:00

Topic: Reflection of light – i. What is reflection of light?
ii. When does it happen?
iii. Types of reflection
iv. Uses of reflection of light, examples?
I have learnt that reflection is the bouncing of light off a mirror surface.

Reflection is also the change in direction of a wave front at an interface between two different media so that the wave front returns into the medium from which it originated.

There are two types of reflection, specular and diffused.
Specular reflection is reflection from a smooth surface. When light strikes this smooth surface, all the reflected rays are in line with each other. An image is formed.
Diffused reflection is reflection from a rough surface. The small bumps and irregularities on a rough surface will cause each of the light rays to reflect n different directions. No image is formed.

Characteristics of Reflection are that the image formed is the same size and shape of the object. It is also a virtual image.

Acknowledgement: http://en.wikipedia.org/wiki/Reflection_(physics)#Laws_of_regular_reflection
http://library.thinkquest.org/27356/p_reflection.htm

Reflection of Light by 2E3 Rachel Ng

2008-06-20T00:20:00.000-07:00

The ray of light which strikes the surface is called the incident ray.
The ray of light which leaves the surface is called the reflected ray.
A line perpendicular to the surface is imagined at the point of reflection. This line is called a normal. And when a ray of light strikes the mirror at a right angle,it is reflected along the same path.

When a ray of light hits a plane mirror at an angle to the normal(called the angle of incident), it is reflected at an equal angle but on the opposite side of the normal(angle of reflection).these two angles are always equal no matter how light rays strike the mirror.
A flat mirror,called plane mirror,is a good reflector of light.

WHAT IS REFLECTION OF LIGHT??
ANS:Reflection is the bouncing off light after hitting a mirror surface.

WHEN DOES IT HAPPEN?
ANS:it happen when the light travel and bounce off after hitting a mirror surface:)

IMAGES IN A PLANE MIRROR
In a plane mirror:
The image is upright
And the image is also of the same size as the object.
The image lies far behind the mirror
But the object is in front of the mirror.
The image is also laterally inverted in a plane mirror.
(Laterally inverted = opposite side)
The image formed is always a virtual image.
(virtual = cannot be capture on screen)

TYPE OF REFLECTION

REGULAR REFLECTION!!
When a parallel beam of light hits a smooth surface such as a plane mirror, it is reflected as a parallel beam. This is called regular reflection. An image is formed with regular reflection. That is. When we look at a smooth surface,we can see an image.
Regular reflection takes place when a parallel beam of light strikes a smooth polished surface and it is reflected back as a parallel beam of light. Reflection from mirror and metallic surface are example of regular reflection.
Regular reflection
On a smooth surface,a parallel beam of light is reflected as a parallel beam.
An image is formed.

DIFFUSE REFLECTION!!
Most surfaces, are usually quite rough. When a beam of light hits a rough surface,the individual rays are reflected in different directions. So no image is formed. This type of reflection is called diffuse reflection.
Diffuse reflection or irregular reflection takes place when a parallel beam of light strikes a rough surface and it is reflected back in different random directions reflected from object such as trees and are example of diffused reflection.
Diffuse reflection
On a rough surface.
A parallel beam of light is reflected as individual rays reflected in different directions
No image is formed.

USES OF PLANE MIRRORS!!

uses of plane mirror:
Help a driver see the traffic behind.
Helps a person check appearance.
Makes s room appear bigger.

USES OF CURVE MIRROR!!
Curve surface can also act as mirrors. Curved mirror can be convex(like the back of a spoon) or concave(like the front of a spoon).The images formed by these mirror are different from those formed by plane mirror. Convex mirror form upright images that are always smaller than the object. They also have large “field of view” ,that is, they allow many thing to be seen.

USES OF CURVE MIRROR!!

Convex mirrors from upright image that are always smaller than the object, They allow many thing to be seen.

Concave mirror form upright magnified if the object is close to the mirror. If the image is further away,the image is inverted.

RESOURSE!!
http://www.google.com.sg/search?hl=en&q=convex+mirror&meta=
http://www.google.com/
Explore your world with science discovery 2 textbook

Electricity by 2E3 Serene Pang

2008-06-20T00:19:00.001-07:00

What is electricity?
Electricity is a naturally occurring force that exists all around us.

How is electricity being produced?
Electricity energy comes from 2 main sources. These are mains electricity and electricity cells.
Main electricity is generated in power stations. The plugs of electrical appliances are inserted into main sockets to obtain this electricity.
Electric cells give out only a little energy. They are called batteries.

What is current?
An electric current is the flow of electrons in one direction in a circuit. We use an ammeter to the size of the electric current. The SI unit for electric current is the ampere (A). The picture shows a ammeter.

What is voltage?
Voltage is a measure of how much energy the electrons receive. To measure voltage, we use voltmeter. The SI unit for voltage is the volt (V). The picture shows a voltmeter.

Uses of electricity
Electricity is the most widely used type of energy in the world. We use it for work and for play, in the home and at work. In the past it mainly provided us with light and heat. Nowadays, the number of electronic appliances has hugely increased, we now use it almost everyday. We also use it for daily applications such as light, fan, etc. It also improves our lives.

Source obtained from textbooks, http://www.teachnet.ie/pcoakley/consumers.htm,

Reflection of Light by 2E3 Syafiq

2008-06-20T00:13:00.000-07:00

I learnt the definition of reflection, the law of reflection, the characteristic of the image formed in a mirror, the different types of reflection, the uses of plain mirrors and curved mirrors and drawing the reflection of diagram during physics lessons.

Definition of reflection: When light rays bounce off the mirror and travel to your eyes.

The law of reflection: The angle of incidence is equal to the angle of reflection.

The characteristic of the image formed in a mirror:

The image formed in a plane mirror is virtual, laterally inverted, upright, same size as the object and the image lies far behind the mirror as the object is in front of the mirror.

The different types of reflection:

( Regular reflection )

When a parallel beam of light hits a smooth surface such as a plane mirror, it is reflected as a parallel beam.

( Diffuse reflection ) When a beam of light hits a rough surface, the individual rays are reflected in different direction and no image is formed.

Uses of plane mirror: It helps the driver to see traffic behind the car, it make a room look bigger and to check the person appearance.

Uses of curved mirror:

(Convex mirror) Convex mirrors form upright images that are always smaller than the object. (e.g. security mirrors are used in shop)

(Concave mirror) Concave mirrors form upright magnified images if the object is close to the mirror. If the object is further away, the image is inverted. (e.g. tool used by dentist)

THE REFLECTION DIAGRAM

Resources: http://images.google.com.sg/ and Science Discovery Science textbook 2.

Reflection of Light by 2E3 Zay Nyein

2008-06-19T18:13:00.000-07:00

I have learn the definition of reflection, the law of reflection , the characteristic of the image formed in mirror, the different types of reflection, the uses of plane mirror and the two different types of curved mirror.

Reflection is the bouncing of light off a mirror and travel to your eyes. The law of reflection: The angle of incidence is equal to the angle of reflection. The image formed in a plane mirror is virtual, upright, laterally inverted, same size as the object and as far behind the mirror as the object is in front of the mirror.

There are two different types of reflection (1) Regular reflection and (2) Diffuse reflection. When the parallel beam of light hits a smooth surface, it is reflected as a parallel beam and the image is formed is called Regular reflection. When a beam of light hits a rough surface, the individual rays are reflected in different directions and the image is not formed is called Diffuse reflection.

The three uses of plane mirror

(1) helps the driver to check the traffic behind

(2) makes a room look bigger and

(3) check the person appearance.

The two different types of curved mirror (1) Concave mirror and (2) Convex mirror.

Concave mirror form upright magnified images if the object is close to the mirror. If the object is further away, the image is inverted e.g. used by dentist to check the teeth.

Convex mirror form upright images that always smaller than the object e.g. security mirrors are used in shops.

Resources
http://images.google.com.sg/ and the Science Discovery 2 (Text book)

Reflection of Light by 2E3 Jocelyn Lee

2008-06-19T18:11:00.000-07:00

After my group and I finished doing the project we has chosen to do( reflection of light), i have learnt how to build good team work with my group members.
I know understand and know more about the reflection of light through this project, such as the law of reflection.
The behavior of the light as it reflects would follow a predictable law known as the law of reflection. Diagrams are use to illustrates the law of reflection. An example of it is:

The ray of light which strikes on the surface is called the incident ray. The ray of light which leaves the surface is called the reflected ray. A line perpendicular to the surface is imagined at the point of reflection the line is called a normal. The angle between the incident ray and the normal is called the angle of incidence. The angle between the reflected ray and the normal is called the angle of reflection.

To summarize,THE ANGLE OF REFLECTION IS EQUAL TO THE ANGLE OF INCIDENCE.

Resources: http://id.mind.net/~zona/mstm/physics/light/rayOptics/reflection/reflection1.html

Sound by 2E2 Syafiqah

2008-06-19T18:10:00.001-07:00

I've learnt something about sound from the sources i had taken and studied,such as borrow books at the library, looking at the science textbook and also searching information on the internet. What i've learnt? I've learnt that sound is a type of energy that were produced when an object vibrates.

Why do we hear sounds?
Humans have three parts, the outer ear, the middle ear and the inner ear.

What does the outer ear do? It collects and funnels the sound to the middle ear. Between the outer ear and the middles ear is a membrane called the eardrum.

What cause the eardrum vibrate?
Sound waves cause the eardrum to vibrate. When the eardrum vibrates, it touches the first of the three tiny bones in the middle ear. This bone vibrates and cause the other two bones to vibrate.

( source taken by book physical science in depth and http://www.worsleyschool.net/science/files/sound/energy.html )

Sound by 2E2 Rosalind

2008-06-19T18:08:00.002-07:00

I learnt What is Sound and What are Sound Waves.

Sound is a type of energy. It is a vibration that travels through the surroundings and enters our ears as sound .

Sound waves are waves which radiate out from their source in circles. The particles of air in the wave move backward and forwards in the same direction as the sound is travelling. These bands of compression and rarefaction move along the spring. This is how s sound wave moves through air, water or solid materials.

Sounds needs to travel through a medium, such as a gas, a liquid or a solid. It cannot travel through a vacuum. This is because sound is a form of energy. In order for sound to move it has to tranfer its energy from one particle to another. If there are no particles, sound cannot travel.

Sound waves are invisible to us, but they can be represented by a machine called an Oscilloscope.

(source taken from book: physical sound IN DEPTH, SOUND)

Sound by 2E2 Shayidah

2008-06-19T18:08:00.001-07:00

I have learnt that Sound is a vibration.
When something makes a noise it is vibrating,and this causes air molecules around it to vibrate too.
These vibrations are transmitted through the air, to our ears, where we preceive them as sound.

Do you know that Thunder is one of nature's loudest sounds!
A nearby thunderclap may reach 120 decibals,equiralent to being within 60 metres of a jet aircraft during take-off.
Volcano eruptions may be the loudest commonly occuring Sounds on Earth,at over 272 dB.

Sound by 2E2 Diyana

2008-06-19T18:07:00.001-07:00

We did on the topic 'Sounds'.I learnt the particular topic in our school science textbook and borrowed some books from the library.I also did some research in the internet about sounds.

Sound is made when something vibrates, it moves back and forth.A vibrating object could be a speaker on a CD player, or your vocal cords or even the strings on a guitar.

As it vibrates, it pushes the air molecules next to it closer together, in patterns corresponding to the movements of the object.

Sound can also be used to do useful jobs. For example; Sound waves sent into the womb of a pegnant woman will be deflected in patterns representing the outline of the fetus within.

(Source taken from www.yahoo.com)

Electricity by 2E4 Nurhakim

2008-06-19T18:04:00.000-07:00

What is the importance of using Electricity?
Electricity is a form of energy. Around us, we are almost surrounded by Electricity.

Examples, Computer & Hand phone. Without Electricity, modern life would be impossible. Imagine there is a Blackout; the life of an electric still goes on as it works on a battery.

Sources of Electricity
There are 2 main sources, main electricity and electric cells.

Main Electricity
Main Electricity is generated by in power plants or power station. There are another 2 types of main electricity.
Re-useable energy
Non-renewable Energy

Electric Cells
Electric Cells gives out very little energy. These are used in many portable electrical devices and are safe to use.

Most of the Electric uses are mainly for…
Communication [To make communication in Space and the Earth]
Electronics [Electronic gadgets]
Telephones [Another type of communication]
Faxes & Modem [Another type of communication]
Radio [Another type of communication]
Television [Another type of communication]
Computers [Another type of communication]
& many more

Electricity by 2E1 Xu Lingyin

2008-06-19T18:00:00.000-07:00

Key point

Electricity is a basic part of nature.
Electricity is a secondary energy source.
Electricity itself is neither renewable or non-renewable.
Applying a force can make them move from one atom to another. These moving electrons are electricity.
A battery produces electricity using two different metals in a chemical solution.
The end that frees more electrons develops a positive charge and the other end develops a negative charge.
A chemical reaction between the metals and the chemicals frees more electrons in one metal than in the other.

Electric current is the rate of charge flow past a given point in an electric
circuit, measured in Coulombs/second which is named Amperes.
The standard abbreviations for the units are 1 A = 1C/s

Voltage is electric potential energy per unit charge, measured in joules per coulomb ( = volts).
It is often referred to as "electric potential", which then must be distinguished from electric potential energy by noting that the "potential" is a "per-unit-charge" quantity.

The difference in voltage measured when moving from point A to point B is equal to the work which would have to be done, per unit charge, against the electric field to move the charge from A to B.
We use a lot of energy - in our homes, in businesses, in industry, and for traveling between all these different places.

What is electricity?
Electricity is a basic part of nature and it is one of our most widely used forms of energy. And it flow of electrical power or charge.

How is electricity being produced?
Electricity is a secondary energy source which means that we get it from the conversion of other sources of energy, like coal, natural gas, oil, nuclear power and other natural sources ,which are called primary sources.The energy sources we use to make electricity can be renewable or non-renewable, but electricity itself is neither renewable or non-renewable. Despite its great importance in our daily lives, most of us rarely stop to think what life would be like without electricity. Yet like air and water, we tend to take electricity for granted. Everyday, we use electricity to do many jobs for us -- from lighting and heating/cooling our homes, to powering our televisions and computers. Electricity is a controllable and convenient form of energy used in the applications of heat, light and power.

In order to understand how electricity charge moves from one atom to another, we need to know something about atoms. Everything in the universe is made of atoms—every star, every tree, every animal. The human body is made of atoms. Air and water are, too. Atoms are the building blocks of the universe. Atoms are so small that millions of them would fit on the head of a pin.
Atoms are made of even smaller particles. The center of an atom is called the nucleus. It is made of particles called protons and neutrons. The protons and neutrons are very small, but electrons are much, much smaller. Electrons spin around the nucleus in shells a great distance from the nucleus. If the nucleus were the size of a tennis ball, the atom would be the size of the Empire State Building. Atoms are mostly empty space.

If you could see an atom, it would look a little like a tiny center of balls surrounded by giant invisible bubbles (or shells). The electrons would be on the surface of the bubbles, constantly spinning and moving to stay as far away from each other as possible. Electrons are held in their shells by an electrical force.

The protons and electrons of an atom are attracted to each other. They both carry an electrical charge. An electrical charge is a force within the particle. Protons have a positive charge (+) and electrons have a negative charge (-). The positive charge of the protons is equal to the negative charge of the electrons. Opposite charges attract each other. When an atom is in balance, it has an equal number of protons and electrons. The neutrons carry no charge and their number can vary.

The number of protons in an atom determines the kind of atom, or element, it is. An element is a substance in which all of the atoms are identical . Every atom of hydrogen, for example, has one proton and one electron, with no neutrons. Every atom of carbon has six protons, six electrons, and six neutrons. The number of protons determines which element it is.

Electrons usually remain a constant distance from the nucleus in precise shells. The shell closest to the nucleus can hold two electrons. The next shell can hold up to eight. The outer shells cans hold even more. Some atoms with many protons can have as many as seven shells with electrons in them.
The electrons in the shells closest to the nucleus have a strong force of attraction to the protons. Sometimes, the electrons in the outermost shells do not. These electrons can be pushed out of their orbits. Applying a force can make them move from one atom to another. These moving electrons are electricity.

BATTERIES PRODUCE ELECTRICITY

A battery produces electricity using two different metals in a chemical solution. A chemical reaction between the metals and the chemicals frees more electrons in one metal than in the other. One end of the battery is attached to one of the metals; the other end is attached to the other metal. The end that frees more electrons develops a positive charge and the other end develops a negative charge. If a wire is attached from one end of the battery to the other, electrons flow through the wire to balance the electrical charge. A load is a device that does work or performs a job. If a load such as a lightbulb is placed along the wire, the electricity can do work as it flows through the wire. In the picture above, electrons flow from the negative end of the battery through the wire to the lightbulb.
The electricity flows through the wire in the lightbulb and back to the battery.

What is Electric Current?
Electric current is the rate of charge flow past a given point in an electric circuit, measured in Coulombs/second which is named Amperes. In most DC electric circuits, it can be assumed that the resistance to current flow is a constant so that the current in the circuit is related to voltage and resistance by Ohm's law. The standard abbreviations for the units are 1 A = 1C/s
.
What is Voltage ？
Voltage is electric potential energy per unit charge, measured in joules per coulomb ( = volts). It is often referred to as "electric potential", which then must be distinguished from electric potential energy by noting that the "potential" is a "per-unit-charge" quantity. Like mechanical potential energy, the zero of potentil can be chosen at any point, so the difference in voltage is the quantity which is physically meaningful. The difference in voltage measured when moving from point A to point B is equal to the work which would have to be done, per unit charge, against the electric field to move the charge from A to B.

Used to calculate current in Ohm's law
Used to express conservation of energy around a circuit in the voltage law
Used to calculate the potential from a distribution of charges
Is generated by moving a wire in a magnetic field

Uses of electricity?
Take a look at all the things we depend on each day that need electricity:
In the kitchen:

Refrigerators

Dishwashers

Stoves

In the family room:
Lamps

Computers

Air conditioning

In the basement or utility room:

Washer and dryer

Furnace

Water heater

Outdoors:

Outdoor lighting

Electric lawn mower

Pool heater

Example:
The United States is a highly developed and industrialized society. We use a lot of energy - in our homes, in businesses, in industry, and for traveling between all these different places.

The industrial sector uses about one-third of the total energy. The residential and commercial sectors combined use even more than this - 40 percent of all energy. These two sectors include all types of buildings, such as houses, offices, stores, restaurants, and places of worship. Energy used for transportation accounts for more than a quarter of all energy.

From this topic,I know Electricity is a form of energy produced by the movement of electrons. Electricity is electrical power or an electric current. This form of energy can be sent through wires in a flow of tiny particles. It is used to produce light and heat and to run motors. Electricity is a basic feature of all matter, of everything in the universe.

Websites
http://www.eia.doe.gov/kids/energyfacts/sources/electricity.html
http://images.google.cn/images?complete=1&hl=zh-CN&rlz=1T4SKPB_zh-CNSG272SG272&q=electricity%20&um=1&ie=UTF-8&sa=N&tab=wi
http://42explore.com/electric.htm

Reflection of Light by 2E4 Wang Si Qian

2008-06-19T17:57:00.000-07:00

flat mirror called a pane mirror, is a good reflector of light. when a ray of light strikes the mirror at a right angle ,it is reflected along the same path. Scientists call this line normal. When a ray of light hits a plane mirror at an angle to the normal(called the angle of incidence),it is reflected at an equal angle but on the opposite side of the normal(the angle of reflection) .These two angles always are always equal no matter how light rays strikes the mirror. This generalization is called the law of reflection .

In a plane mirror, - the image is upright and of the same size as the object
-the image lies as far behind the mirror as the object is in front of the mirror.
-an image is laterally inverted.
-the image formed is always a virtual image.

Type of reflection -regular reflection and diffuse reflection

Regular reflection:
-when a parallel beam of light hits a smooth surface such as a plane mirror, it is reflected as a parallel beam.
-an image is formed.

Diffuse reflection:
-when a beam of light hits a rough surface, the individual rays are reflected in different directions.
-no image is formed.

The use of plane mirror: -people use plane mirrors to check their appearance.
-plane mirrors on walls make the room bigger.
-the rear view mirror of a car helps the diver to see traffic behind the car.
-two plane mirrors are used in a periscope to reflect and change the direction of light.
-a telescope uses mirrors to produce very clear image.

Laws in this topic
–light travels in straight lines.
-for reflection in a plane mirror, the angle of incidence is equal to the angle of reflection.
-the angle of incidence=the angle of reflection.

Resources are from: textbook and www.treemo.com/users/somniumfate/channel/item/62506

Colours of Light by 2E2 Lee Yen Ting

2008-06-19T17:54:00.000-07:00

Colours of light.
I learnt that when a beam of white light passes through a glass prism, the light splits up into the colours we in a rainbow. These colours are called the spectrum of white lights. Dispersion of light is when the separation or splitting of white light into its separate colours.

White light consists of seven colours, we should be able to get white light again by combining the colours together. Here are the ways:
One is by spinning a colours wheel: when the wheel is turned quickly, the colours appear to mix and the wheel looks white.

Primary colours are colours that can be obtained by mixing with just three colours – red, Blue and green. Mixing all three primary colours gives white light.

By mixing the primary colours two at a time gives the following colours:
Red + Blue = magenta
Red + green = yellow
Blue + green = cyan

The key points is that Rainbow is formed when a beam of white light passes through a glass prism and the light splits up into the colours we see in a rainbow. Light of different colours can be mixed together to produce other colours.

The spectrum consists of seven colours: Red, Orange, Yellow, Green, Blue, Indigo and Violet. We could remember the order as a boy’s name: ROY G BIV.
These colours formed as a colour wheel and when the colours wheel spins, the colours appear to mix and the wheel looks white as mention above how to combine the colours together to get white light again.

These information can be found in Explore Your World with SCIENCE DISCOVERY 2 page 128 – 130.

Colours of light by 2E2 Billy A.

2008-06-19T17:52:00.000-07:00

How are colours being produced? The colour are produced when light pass through a prism. The process is called dispersion. The most familiar example of dispersion is probably a rainbow, in which dispersion causes the spatial separation of a white light into components of different wavelengths (different colors).

However, dispersion also has an impact in many other circumstances: for example, it causes pulses to spread in optical fibers, degrading signals over long distances; also, a cancellation between dispersion and nonlinear effects leads to soliton waves. Dispersion is most often described for light waves, but it may occur for any kind of wave that interacts with a medium or passes through an inhomogeneous geometry (e.g. a waveguide), such as sound waves. Dispersion is sometimes called chromatic dispersion to emphasize its wavelength-dependent nature.

Sunlight is often called white light, since it is a combination of all the visible colours. Since the index of refraction is different for each colour, the angle of refraction will be different for each colour when the light passes from air into glass or other transparent material. This is according to Snell's Law. (See Snell's Law for the Refraction of Light for more information.)

Now if the piece of glass has parallel sides--such as with a window--the light will return in the same direction that it entered the material. But if the material is shaped like a prism, the angles for each colour will be exaggerated, and the colours will be displayed as a spectrum of light

The visible colours are in the order of the spectrum. You can remember the order by the name ROY G. BIV. Note that in the illustration above, the colours are distinctly separated. In realty, they blend into each other, such that there are colours in between. For example, there is red-orange in between red and orange. To get it back just reverse the process.

The primary colours red, blue, and green. these colours are then mixed to make secondary colours and if the three colours are mixed, it will make the colour white.

In optics and physics, Snell's law (also known as Descartes' law or the law of diffraction), is a formula used to describe the relationship between the angles of incidence and refraction, when referring to light or other waves, passing through a boundary between two different isotropic media, such as water and glass. The law says that the ratio of the sine’s of the angles of incidence and of refraction is a constant that depends on the media.

In optics, the law is used in ray tracing to compute the angles of incidence or refraction, and in experimental optics to find the refractive index of a material.

Refraction of light at the interface between two media of different refractive indices, with n2 > n1. Since the velocity is lower in the second medium (v2 < v1), the angle of refraction θ2 is less than the angle of incidence θ1; that is, the ray in the higher-index medium is closer to the normal.
Named after Dutch mathematician Willebrord Snellius, one of its discoverers,

Snell's law states that the ratio of the sine’s of the angles of incidence and refraction is equivalent to the ratio of velocities in the two media, or equivalent to the opposite ratio of the indices of refraction:
or
Snell's law follows from Fermat's principle of least time, which in turn follows from the propagation of light as waves.

SOURCE
-wikipedia
-books
-encarta
-my brain

Reflection of Light by 2E4 Fang Shu Yang

2008-06-19T17:50:00.000-07:00

When reflection of light photoemission to two kind of different natures, then has part of light, from the interface shoots in the original nature the phenomenon, is called the reflection of light. law of reflection:

(1) incident ray, reflect rays and normal on identical plane mirror, and incident ray, reflect rays in normal both sides.

(2) the incidence angle is equal to the reflection angle. the surface smooth object, easy to form the light the regular reflection, forms the dazzling glare, instead looks at not the clear object. in the usual situation may distinguish shape and the existence the object, therefore is as a result of the light diffusion. after sunset, can see the object temporarily, is therefore because in the air the dust causes the light diffusion. Regardless of being the regular reflection or the diffuse reflection, must observe the law of reflection。

When the light shines after the object on, some part of light have been absorbed (with light frequency related), other cannot the light which absorbs be the reflected light. The reflection divides into the regular reflection and the diffuse reflection.

Reflection of Light by 2E3 Kho Wei Xian

2008-06-19T17:47:00.002-07:00

After the first semester, I have learnt a lot of thing about the reflection of light. The law of reflection, the types of reflection, uses of mirrors and image in a plane mirror.

Reflection is the bouncing off light after hitting a mirror surface. The reflection of light can be represented by the reflected diagram. A plane mirror is a good reflector of light. The ray of light approaching the mirror is known as the incident ray (labeled i in the diagram). The ray of light which leaves the mirror is known as the reflected ray (labeled r in the diagram). At the point of incidence where the ray strikes the mirror, a line can be drawn perpendicular to the surface of the mirror. This line is known as a normal line. (labelled N in the diagram)

The normal line divides the angle between the incident ray and the reflected ray into two equal angles. The angle between the incident ray and the normal is known as the angle of incidence. The angle between the reflected ray and the normal is known as the angle of reflection. When a ray of light hit a plane mirror and when the light is reflected, the angle of incidence and the angle of reflection is the same. This is called the law of reflection.

I also learnt that in a plane mirror,
The image formed is upright and it is the same size as the object,
The image lies far behind the mirror as the object is in front of the mirror,
The image is laterally inverted
The image is virtual(It cannot be captured on the screen)

There are two types of reflection, Regular and Diffuse reflection.
Regular reflection is when parallel beam of light hits a smooth surface and is reflected as a parallel beam.
Diffuse reflection is when a beam of light hits a rough surface, the individual ray are reflected in different directions. There is image formed in Regular reflection and there is no image formed in Diffuse reflection.

I also learnt the uses of the mirrors. There are three types of mirrors, Plane mirrors, and Convex, Concave mirrors which are under Curved mirrors.

Plane mirrors helps the driver to see traffic behind, make a room appear bigger and let a person check their appearance.

Convex mirrors form upright images that are always smaller than the object. They also allow many things to be seen. Convex mirrors are used in shops for security reasons, and also helps the drivers to see object around the corner.

Concave mirrors form upright magnified images if the object is close to the mirror. The image I inverted if the object is further away. Concave mirrors are used to reflect light into a microscope and help the dentists to check teeth conditions.

I have also found out that other than Regular and Diffuse reflection, there are other types of reflection such as Retro reflection, Complex conjugate reflection, Neutron reflection, Sound reflection, Seismic reflection.

Acknowledgements: http://www.glenbrook.k12.il.us/GBSSCI/PHYS/Class/refln/u13l1c.html
http://en.wikipedia.org/wiki/Reflection_(physics)
Explore Your World With Science Discovery 2

Done By: KHO WEI XIAN (25)

Sound by 2E1 Priscilla Gwee

2008-06-19T17:47:00.001-07:00

Sound is a form of energy. Sound is the quickly varying pressure wave within a medium.

Sound is produced by the vibration of objects. When object vibrate, they move backwards and forwards very quickly. Frequency is the number of vibrations in one second. Frequency is measured in hertz (Hz).If the frequency is 100Hz, it means that it produced 100 vibrations every seconds.

The medium affect the speed of sound. Thus it will also affect the sound.

The examples of stuff producing sound are instruments, insects, phones, human talking, music from CD player, sound of the fan, traffic noise and alarm clock.

Sound travels in the form of waves. Sound travels through matter (solids, liquids and gases). Sound toke time to travel from one place to another. The speed of the sound in the air is about 330 metres per seconds.

We can also find things with sound. For example, if we make a loud noise in a large room, there will be echo. The sound we make travels to the walls and is reflected back to our ears. Echoes are also able to find objects underwater. This is called echolocation.

Some uses of echolocation is to find submarines from surface ships, to measure the depth of the sea and to find shoals of fish in fishing boats. Animals like bats and dolphins also use echolocation to find food and where they are going.

Websites: www.yahoo.com
www.google.com
www.ask.com

Textbook Resource: Explore Your World With Science Discovery 2.

Refraction of Light by 2E2 Chee Hui Juan

2008-06-19T17:45:00.000-07:00

REFRACTION OF LIGHT
Qn: What is refraction of light?
Refraction is the bending of light due to the change of its speed when it passes from one medium to another of a different optical densities.

Qn: When does it happen? How and when will light bend?
The bending occurs because the speed in which light travels through a substance depends on the substance’s density. Light only bends when it passes from a substances of one density into a substances of a different density. Since light travels slower in water then in air, water is said to have a greater optical density than air.

Qn: What it refractive index?
It is the ratio of speed in light in vacuum and speed of light in the material.

Qn: Effects of refraction?
Bending of objects
Objects partially submerged in water appear bent, shifted and magnified.

Apparent thickness
Glass blocks appear less thick than they actually are.

Apparent depth
Swimming pools appear shallower than they actually are.

Apparent position
At dawn or dusk, then Sun appears to be above the horizon at its apparent position for about four minutes longer than it really is.

Source; textbook resource and http://en.wikipedia.org/wiki/Refraction

Colours of Light by 2E3 Ho Zong Hua

2008-06-19T17:42:00.000-07:00

Dispersion of White Light and How are colours produced
Sunlight may appear white, but it is actually made up of a mixture of seven colours. When the sunlight passes through the raindrops, the raindrops split the sunlight into a range or a spectrum of colours. The colours that make up the spectrum are red, orange, yellow, green, blue, indigo and violet. The spitting of white light into a range or a spectrum is called the dispersion of white light.

Dispersion of White Light and How are colours produced
When a beam of white light enters a prism, it slows down and is refracted. The white light is then split into seven different visible colours of light. Which are red, orange, yellow, green, blue, indigo and violet. The seven different colours of light, which make up white light, slow down at different rates. In other words, the different colours of light are refracted or bent at different angles.

Point 2
How to get rainbow colours and to recombine it again
What is primary colours
What are the effects of mixing colours

As the refracted colours of light leave the prism, they are bent again, but not in their original paths. This is because the face of the prism through which the light leaves is not parallel to the face through which it enters.
To prove that white light is a mixture of different colours, another prism can be used to recombine the colours of its spectrum.
Another way of combining the different colours of spectrum is by spinning a rainbow-coloured disc called Newton’s disc.

Primary colours are green, red and blue; these three colours when mixed will form the white light.
Cyan, yellow and magenta are called secondary colours. They are produced by mixing any two of the three primary colours.
Cyan = blue + green
Yellow = red + green
Magenta = red + blue
Mixing all the three primary colours will give the white light
Red + blue + green = white
By using different brightness we can create all the colours of the rainbow and many other colours that go to make up our multicolored world.

Refraction of Light by 2E1 Karthik

2008-06-19T17:41:00.000-07:00

Refraction is the change in direction of a wave due to a change in its speed. This is most commonly seen when a wave passes from one medium to another.

Refraction of light is the most commonly seen example, but any type of wave can refract when it interacts with a medium, for example when sound waves pass from one medium into another or when water waves move into water of a different depth.

Refraction can be seen when looking into a bowl of water. If a person looks at a straight object, such as a pencil or straw, which is placed at a slant, partially in the water, the object appears to bend at the water's surface. This is due to the bending of light rays as they move from the water to the air. Once the rays reach the eye, the eye traces them back as straight lines (lines of sight). The lines of sight (shown as dashed lines) intersect at a higher position than where the actual rays originated. This causes the pencil to appear higher and the water to appear shallower than it really is.

Another example of refraction

Index of Refraction
The index of refraction is defined as the speed of light in vacuum divided by the speed of light in the medium.

The indices of refraction of some common substances are given below with a more complete description of the indices for optical glasses given elsewhere. The values given are approximate and do not account for the small variation of index with light wavelength which is called dispersion

Refraction of Light by 2E4 Zhang Meiting

2008-06-19T17:39:00.000-07:00

Download the original attachment
Refraction Of Light
In this blog reflection, I have chosen refraction of light as my topic. In this topic, I have learnt that refraction of light is when the light goes in or out of the glass, it changes direction because the rays bend. One example I have learn is when I put a cup of water on the table with a straw inside, I realise that the straw has cut into half but as when I take the straw out of the cup, again I realise that the straw is still in it original shape and length. And this experiment had showed me that light changes direction when it passes from one transparent material into another.

And in this particular topic, I know that light bends because its speed changes as it moves from 1 transparent material to another. Also, light travels slower in more dense materials than in less dense materials that why light travels slower in glass than in air. So, when a beam of light passes from air into a glass block, it slows down and bends towards the normal but when the beam of light comes out of glass into air, it will bend away from the normal.

From this particular topic, I learn that when the boundary of 2 optical media, there will be a sudden change in the speed of light to bend, resulting in refraction. Since I know that refraction is caused by a change in speed of light, the relationship between the angle of incidence and the angle of reflection has to be related to this change in speed of light in a medium.

For the effects of refraction I learn so far, a swimming pool appears shallower than it really is. This is because light from an object bends as it comes out of water. But human brain thinks that the light has moved in a straight line. So, the object appears to be at a higher position than it actually is.

The key points of this topic are, light is bend or refracted when it passes from one transparent material into another, such as from air to glass and vice versa. For the refraction I have learn, there are two effects, which are, an object in water appears nearer to the surface than it really is and an object such as a stick placed in water appears to be bent.

All these are found in:
sec2 textbook
sec2 theory workbook
handout
sec4 physics textbook
http://hyperphysics.phy-astr.gsu.edu/hbase/geoopt/refr.html

Refraction of Light by 2E2 Edna Chew

2008-06-19T17:36:00.000-07:00

Refraction of Light
Refraction is the bending of a wave when it enters a medium where its speed is different. The refraction of light when it passes from a fast medium to a slow medium bends the light ray toward the normal to the boundary between the two media.
If you have ever half submerged a pen into water, you have probably noticed that the pen appears bent at the point it enters the water.
This optical effect is due to refraction.

When light travels through air it travels at 186,000 miles per second. As the light encounters a water surface some of the light is reflected and some of the light passes into the water. Upon entering the water, however, the light slows down by 46,000 miles per second. This change in speed causes the direction of the light ray to change. When we look at a pencil in a glass of water the light from the pencil in the water is being refracted, so it appears in a different location.

How refraction happens depends on the refractive index of the mediums and the angle between the light ray and the line perpendicular (normal) to the surface separating the two mediums (medium/medium interface).

The angle between the light ray and the normal as it leaves a medium is called the angle of incidence. The angle between the light ray and the normal as it enters a medium is called the angle of refraction.

When light passes from a substance of lower optical density to a substance of higher optical density the light is refracted at a smaller angle relative to the normal. (Figure 1)

When light passes from a substance of higher optical density to a substance of lower optical density the light is refracted a larger angle relative to the normal. (Figure 2)

Figure 1 Figure 2

Refraction is also responsible for rainbows and for the splitting of white light into a rainbow-spectrum as it passes through a glass prism. Glass has a higher refractive index than air and the different frequencies of light travel at different speeds (dispersion), causing them to be refracted at different angles, so that you can see them. The different frequencies correspond to different colors observed.
While refraction allows for beautiful phenomena such as rainbows, it may also produce peculiar optical phenomena, such as mirages and Fata Morgana. These are caused by the change of the refractive index of air with temperature.
Refractive Index
The refractive index of a medium is a measure for how much the speed of light (or other waves such as sound waves) is reduced inside the medium.
The refractive index n of a medium is defined as the ratio of the phase velocityc of a wave phenomenon such as light or sound in a reference medium to the phase velocity vp in the medium itself:

Acknowledgement:
http://en.wikipedia.org/
http://library.thinkquest.org/27066/lightrays/nlrefraction.html
http://www.ps.missouri.edu/rickspage/refract/refraction.html
http://hyperphysics.phy-astr.gsu.edu/hbase/geoopt/refr.html
http://ww2010.atmos.uiuc.edu/(Gh)/guides/mtr/opt/mch/refr/more.rxml

Reflection of Light by 2E4 Chanita

2008-06-19T17:31:00.001-07:00

Light of "Reflection": is "a ray of light bounces off of a mirror.

Types of reflection
Regular Reflection
- with surfaces so smooth are smaller than the wavelength of light, the law of reflection applies on a large scale. All the light traveling in one direction and reflecting from the mirror is reflected in one direction.

Diffuse reflection
– with light being reflected in all directions. If the irregularities on the surface of an object are larger than the wavelength of light, which is usually the case, the light reflects off in all directions.

Uses of reflection of light
Convex mirrors are often used in shops as security mirrors because of the type of image produced by that mirror. The image is smaller but shows a wide angle view of the shop.
Concave mirrors are often used in torch lights. The light travels in all directions from the light globe towards the mirror behind it. The rays are then reflected by the mirror and they form a beam of light (a bundle of parallel rays).

Facts:
1. The woman's image is as far behind the flat mirror as she is in front of it. >>>
2.The "woman" in the mirror is combing her hair with her left hand.>>>
When the water is still, reflection is specular. The image blurs when the water is rough

Images in convex mirrors are always smaller
Images in concave mirrors are always bigger

Do You Know that:?
*Light slows down, bends toward the normal and has a shorter wavelength when it enters a higher (n) value medium.
*The Rainbow is a reflection of perfect balance of the physical world

Thinking Time:
All you brainiacs out there, if light reflect off an object... then what colour is the object itself? If white light contains all the colours of the visible spectrum, and say, it reflects off of an object that is red, the object itself absorbs all the colours of the spectrum except red. So then is that object in fact red? Or is it every other colour except red? What about a 'black’ light. If the color black lacks all colours, why then when you shine a black light on an object, it appears as its 'negative' color, such as reds or yellows appear green. Not all colors but many colors exhibit this phenomenon. An object that is "white' in color glows almost fluorescent in black light... What is it exactly are we seeing when we see the 'colour' of an object?
Answer: The colour we are seeing is in fact the light being reflected off the object as well as the reception of our rod and cone cells in the retina of the eye. The cone cells are the ones that respond to different colors. There are groups of cone cells that respond to red, or blue or yellow so basically what we 'perceive' as color depends on both these factors. And really, perception is on an individual basis. Theoretically, what you perceive as red, I may perceive as blue. It is very much possible. Colours, I think are an illusion that we create with our brains. They are just that. They themselves have no 'color'. Its like our brain receives this upside down weird black and white photo, and puts it upright, colours it up to make it attractive. And that is what we see as 'beautiful' and colourful. As for reality...that, we may never know.

Game: http://www.phy.ntnu.edu.tw/oldjava/optics/mirrorgame_e.html

Resources:
www.yahoo.com/question/index?qid=20070819060134AAanM50 - 47k –
http://www.google.co.th/

Refraction of Light by 2E1 Teresa Zhou

2008-06-19T17:29:00.000-07:00

Refraction
Refraction is the change in the direction of light. Refraction is caused by the change in speed experienced by a wave when it changes medium, such as when light passes from one transparent material into another, like from air to glass, air to water, or from water to glass, and also in the opposite directions glass to air.

There is an incident ray (drawn perpendicular to the watefronts), which is a ray that shows the direction which light travels as it approaches the boundary. Similarly, refracted ray (drawn perpendicular to the wavefronts is a ray which shows the direction which light travels after it has crossed over the boundary.

During refraction, light bends first on passing from air to glass, and again on passing from glass to the air again. Light travels faster when moving from a less dense material to a denser material, such as from the air to the glass, and it bends away from the normal, but however when light moves from the glass to the air, which is from a denser material to a less dense material, it travels slower and bends towards the normal.

Refraction has some unusual effects in everyday life. Refraction can cause words to appear nearer to the surface of the glass than they actually are, so the glass block appears to be thinner than it really is. The object can also appear to be at a higher position than it actually is when under the water, like when in a swimming pool, where we think that it appears shallower than it really is. Refraction is even responsible for causing rainbows, splitting their light into the rainbow-spectrums!

Some fun facts about refraction:
Try putting a straw into a glass of water. It would appear bent.
This is because light is moving from a less dense material to a denser material, therefore it bends further away from the normal. In our eyes, we would see that it appears bent.

When a hunter wants to spear a fish that is under water, being experienced, he would aim at a little lower from where the fish is.
Light is moving from air to water, therefore light bends away from the normal. If he were to hit exactly where the fish is, he would miss and end up hitting nothing, so he has to hit lower to hit exactly where the fish is.

Try taking a photo of the waves in the ripple tank; you will see some stripes appearing on your photograph.
Ripples travel from the left and pass over a shallower region inclined at an angle to the wavefront. The waves travel more slowly in the shallower water, so the wavelength decreases and the wave bends at the boundary. The dotted line represents the normal to the boundary. The dashed line represents the original direction of the waves. The phenomenon explains why waves on a shoreline never hit the shoreline at an angle.

The angle of light refraction to create a Rainbow is 42 degrees to the eye of the observer.
The same theory, as when light moves from less dense material to a denser material. It travels faster, and it is bent away from the normal, therefore 42 degrees to the eye of the observer.

Sound by 2E1 Aziizah

2008-06-19T17:22:00.000-07:00

What is sound?
Sound is the quickly varying pressure wave within a medium. We usually mean audible sound, which is the sensation (as detected by the ear) of very small rapid changes in the air pressure above and below a static value. This "static" value is atmospheric pressure (about 100,000 Pascals), which does nevertheless vary slowly, as shown on a barometer. Associated with the sound pressure wave is a flow of energy. Sound is often represented diagrammatically as a sine wave, but physically sound (in air) is a longitudinal wave where the wave motion is in the direction of the movement of energy. The wave crests can be considered as the pressure maxima whilst the troughs represent the pressure minima.

ii. How is sound being produced?
Sound is produced when the air is disturbed in some way, for example by a vibrating object. A speaker cone from a high fidelity system serves as a good illustration. It may be possible to see the movement of a bass speaker cone, providing it is producing very low frequency sound. As the cone moves forward the air immediately in front is compressed causing a slight increase in air pressure, it then moves back past its rest position and causes a reduction in the air pressure (rarefaction). The process continues so that a wave of alternating high and low pressure is radiated away from the speaker cone at the speed of sound.

iii. What affects sound?
Vibrations and frequency affects sound. Vibrations produce sounds. When objects vibrate, they move backwards and forwards very quickly. The number of vibrations in one second is called the frequency.

iv. Examples of stuff producing sound?
Drums
Guitar
Bee
Trumpet
Saxophone

Summary:
Sound is a form of energy.
The vibration of objects produces sounds.
Frequency is the number of vibrations per second. Frequency is measured in hertz {Hz).

Sources:
http://www.tek-ltd.com/school2.htm

Refraction of Light by 2E1 Bank

2008-06-19T17:21:00.000-07:00

Refraction
The change in direction of light is called refraction. In an experiment where a straw in a glass of water appears bent, it is because of refraction, light changes direction when it passes from one transparent material into another, like from air to glass, from air to water, from water to glass and in the opposite direction, glass to air.

Light will bend first on passing from one material to another; it will first pass from air to glass and again on passing from the glass to the air again. When light moves from air to glass, it is refracted towards the normal. When the light moves from the glass to air, it is refracted away from the normal.

Light bends because its speed changes as it moves from one transparent material to another. Refraction can be seen when looking into a bowl of water. Air has a refractive index of about 1.0003, and water has a refractive index of about 1.33. If a person looks at a straight object, such as a pencil or straw, which is placed at a slant, partially in the water, the object appears to bend at the water's surface. This is due to the bending of light rays as they move from the water to the air.

We use refraction in mirrors, swimming pools, and many others. Refraction is also responsible for rainbows and for the splitting of white light into a rainbow-spectrum as it passes through a glass prism. Glass has a higher refractive index than air and the different frequencies of light travel at different speeds (dispersion), causing them to be refracted at different angles, so that you can see them. The different frequencies correspond to different colors observed.

Refraction is a topic that I have learnt this term. I never knew that when a straw looks bent in a glass of water, it is actually the cause of refraction. I find it interesting and something new to me.
Throughout the term, I have learnt how to draw the process of refraction and know the definition of refraction. I have learnt how refraction can happen like when light passes through from a less dense material to a denser material or the other way round.
Refraction is always all around me but I never realise it. I am glad to have learnt refraction this term.

Reflection of Light by 2E4 HA SEONG EUN

2008-06-19T17:20:00.000-07:00

Reflection of light occurs when the waves encounter a surface or other boundary that does not absorb the energy of the radiation and bounces the waves away from the surface. The simplest example of visible light reflection is the surface of a smooth pool of water, where the light is reflected in an orderly manner to produce a clear image of the scenery surrounding the pool.
When does it happen
Reflection of light occurs when the waves encounter a surface or other boundary that does not absorb the energy of the radiation and bounces the waves away from the surface. This tutorial explores the incident and reflected angles of a single light wave impacting on a smooth surface.
Types of reflection
Regular reflection occurs when incident parallel rays are also reflected parallel from a smooth surface. If the surface is smooth, parallel incident rays are no longer parallel when reflected. This results in diffuse.
The laws of reflection apply to diffuse reflection. The irregular surface can be considered to be made up of a large number of small planar reflecting surfaces positioned at slightly different angles. Indirect (or diffuse) lighting produces soft shadows. It produces less eye strain than harsher, direct lighting.
Uses of reflection
A refracting telescope uses convex lenses to gather a large amount of light and focus it onto a smaller area. Refracting telescopes use two lenses—an eyepiece lens and an objective lens. When light passes through the objective lens, the lens focuses the light at a certain distance away from the lens. This distance is called the focal length of the lens.
Plane mirror
The rear view mirror of a car helps the drivers to see traffic behind the car.
Plane mirrors on walls make a room look bigger.
Convex mirror
Security mirrors are used in shops.
Concave mirror
A concave mirror is used to reflect light into the microscope.

Reflection of Light by 2E3 Lim Jun Jie

2008-06-19T17:18:00.000-07:00

Reflection of light
What is reflection of light?
Reflection of light is, light rays bounce of the mirror and travel to your eyes, this bouncing of light off a mirror is called reflection.

When does it happen?
Reflection of light (and other forms of electromagnetic radiation) occurs when the waves encounter a surface or other boundary that does not absorb the energy of the radiation and bounces the waves away from the surface.

Types of reflection.
Diffuse reflection
When light strikes a rough or granular surface, it bounces off in all directions due to the microscopic irregularities of the interface. Thus, an 'image' is not formed. This is called diffuse reflection. The exact form of the reflection depends on the structure of the surface.

Retro reflector
A simple retro reflector can be made by placing three ordinary mirrors mutually perpendicular to one another (a corner reflector). The image produced is the inverse of one produced by a single mirror. A surface can be made partially retro reflective by depositing a layer of tiny refractive spheres on it or by creating small pyramid like structures. In both cases internal reflection causes the light to be reflected back to where it originated. In this application perfect retro reflection is not desired, since the light would then be directed back into the headlights of an oncoming car rather than to the driver's eyes

Complex conjugate reflection
Light bounces exactly back in the direction from which it came due to a nonlinear optical process. In this type of reflection, not only the direction of the light is reversed, but the actual wave fronts are reversed as well.

Uses of reflection of light, examples?
Some uses of reflection is for people to check their appearance a mirror at home, allow drivers to see the traffic behind the car a rear view mirror, to allow owners of shops to see angles of their shops which they can’t see a security mirror, magnifies image a dentist mirror.

Adapted from:
http://en.wikipedia.org/wiki/Reflection_(physics)
http://micro.magnet.fsu.edu/primer/lightandcolor/reflectionintro.html

Electricity by 2E3 Bernard Kay

2008-06-19T17:17:00.000-07:00

What is electricity
Electricity is a form of energy.It is very convenient because it can be changed to other forms of energy.Electrical energy is changed to sound energy in radios,to heat energy in rice cookers and to kinetic energy in radios,to heat energy in rice cookers and to kinetic energy in electric fans.

How is electricity produced
Electricity is produced generated in power stations.The plugs of the electrical appliances are inserted into mains sockets to obtain this electricity.Main electricity supplies a lot of energy.It can give us an electric shock which can kill us.
Electricity can also be produced from fossil fuels,hydro dams,static electricity.

Uses of electricity
Electricity is used to power up our daily usage such as.Computers,lamps,air conditioning,furnace,water heater

Reflection of Light by 2E3 Fong Lai Guan

2008-06-19T17:14:00.001-07:00

WHAT IS REFLECTION OF LIGHT?
Reflection of light is light ray that neither transmitted nor absorbed, but bounced back to our eyes from the surface of the medium they encounter. This happened when incident ray approaches a surface of a reflecting medium, such as a mirror, this ray is then bounces back as reflected ray.

TYPE OF REFLECTION
There are three of reflections. They are diffuse, mirror and retort reflection.
Diffuse reflection occurs when light strikes rough surface such as clothing and foliage. These surfaces cause the light to scatter in all direction. No reflection formed.
Mirror reflection occurs when light strikes surface that are smooth and glossy. The light reflects off the surface at an equal, but opposite angle to the source. Reflection is formed.
Retort reflection occurs when surfaces return a portion of directed light back to its source.

USES OF REFLECTION
For looking at yourself, making look bigger than it suppose to and checking of shoplifter etc.
I learn that there are more to learn from the internet than the textbook. The information the textbook is too limited.
Information from:http://www.tpub.com/neets/tm/106-3.htm

Refraction of Light by 2E4 Lavanya

2008-06-19T17:08:00.000-07:00

REFRACTION
WHAT IS REFRACTION OF LIGHT?
WHEN DOES IT HAPPEN?
HOW AND WHEN WILL LIGHT BEND?
WHAT IS REFRACTIVE INDEX?
EFFECTS OF REFRACTION

Refraction of light refers to the change in the
direction of light.
Refraction of light occurs when it passes from
one transparent material into another.
3a.When light moves from glass to air (a less dense
material), it speeds up and is refracted away from
the normal.
Light twists outward when entering
Medium of lower index of refraction
3b. When light moves from air to glass (a denser material),
it slows down and is refracted towards the normal.

Light twists inward when entering
medium of higher index of refraction
4. The effects of refraction are causing an object to appear nearer than it actually is when a transparent material is on top.

Refraction of light by 2E4 Chua Xue Ting

2008-06-19T17:07:00.001-07:00

Refraction of light is not difficult to learn. Refraction happen everywhere, and anytime it can happen when a person uses a mirror to see their look, and can happen when a light shine on a metal object. Refraction is a bouncing off light through refraction mirror. There are two type of refraction mirror, concave and convex mirror. Concave mirror is use as Security
Mirror and use at blind corner. Convex mirror is use as face mirror. Refraction of light cannot occur when there is no refracted object.
There is a lot of refraction object- example metal spoon, shiny watch and keychain. These object is a good refraction object. Normally, a good refraction object is easier to catch fire than non refraction. This is because refraction object get more light to heat up.
Light rare cause the light to bend when pass through the glass. This is because the air is denser than the glass, so when light rare passes through the glass.

Sound by 2E1 Ng Xinying

2008-06-19T17:02:00.000-07:00

In this topic I've learnt about what causes sound, the transmisson of sound,more things about the human
ears, the pitch and music and the importance of soun in the society.
Now im going to summarise what i have learnt about the topic.
I have learnt that....
Sound is a form of energy.
Sounds are produced by the vibration of objects.
Frenquency is the number of vibrations per sec. And they are measured in Hertz(Hz)
Sound travels through matter -Liquid,Solid and Gas.
Sound takes time to travel from one place to another. the speed of sound in the air is about 330 metres per second.
Sound travels in form of waves.
The human ear can hear only a limited range of sound frequencies.
The ear is a sound detector that has 3 main parts, the outer ear,the inner ear and the middle ear.
Sound is important in society for communication as a warning and as a pleasure.
Noise is sound that is loud and unpleasant.
the loudness of sound is measured as decibels(dB).
Sound above 90dB can cause damage to our ears.
Ear protectors and noise barriers are two ways of reducing loud noise.
Sound frequencies higher than those that can be detected by humans are called ultrasound.
Ultrasound has many application in industry and medicine.
the higness and lowness of a musical note is called its pitch.
a note with a low pitch is called a low frenquency. A note with a high pitch is called a high frequency.
For wind instruments,the shorter the column of air, the higher the pitch of a note.
For string instruments,the shorter the string the higher pitch of a note.
The vocal cords in our throats produce sounds.
Here's a fact!
Have you experienced a ringing sound in your ears after listening to loud music or noise? People who are continually exposed to loud sounds develop a permanent ringing sound. this affliction ehich cannot be cured is called tinitus.