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
Showing posts with label 2e1. Show all posts
Showing posts with label 2e1. Show all posts
Friday, June 20, 2008
Colours of Light by 2E1 Jason
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]
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]
Refraction of Light by 2E1 Shahir
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.
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.
Colours of Light by 2E1 Vaishnavi
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
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/
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
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.
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
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
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
Sound by 2E1 Shafiatul
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
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
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
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 Marcus Choo
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.
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.
Refraction of Light by 2E1 Jeong Seok Young
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
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
Sound by 2E1 Ebel
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
[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
Electricity by 2E1 Chen Meng
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
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
Sound by 2E1 Tan Hui Yu
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
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
Sound by 2E1 Desiree Ang
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).
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.
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.
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!
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)
Thursday, June 19, 2008
Electricity by 2E1 Xu Lingyin
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.
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
Sound by 2E1 Priscilla Gwee
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.
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 2E1 Karthik
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 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 2E1 Teresa Zhou
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.
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
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
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
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