LIGHT

Visible, or white, lights is a form of electromagnetic radiation occurring between infra-red and ultraviolet waves in the electromagnetic spectrum. White light is a mixture of many different colors of light, each with its own wavelength. When white light passes through a prism it is refracted and split up into its various wavelength, so that all the colors can be seen separately. These colours make up the visible spectrum. Our eyes detect colours by recognizing the different wavelengths of visible light.

OPTICS

Refraction is the bending of light rays when passing through a surface between one transparent material and another. It is described by Snell's Law:

where θ₁ is the angle between the ray and the surface normal in the first medium, θ₂ is the angle between the ray and the surface normal in the second medium, and n₁ and n₂ are theindices of refraction, n = 1 in a vacuum and n > 1 in a transparent substance.

An example of refraction light. The straw
appears bent, because of refraction of light  as it
enters liquid from air.

When a beam of light crosses the boundary between a vacuum and another medium, or between two different media, the wavelength of the light changes, but the frequency remains constant. If the beam of light is not orthogonal (or rather normal) to the boundary, the change in wavelength results in a change in the direction of the beam. This change of direction is known as refraction.

The refractive quality of lenses is frequently used to manipulate light in order to change the apparent size of images. Magnifying glasses, spectacles, contact lenses, microscopes andrefracting telescopes are all examples of this manipulation.