Colours of Light by 2E4 Jun Min Jung

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