Colours of light by 2E2 Billy A.

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

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

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

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

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

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

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

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

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

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

SOURCE
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