Refraction of Light Through a Glass Prism
We have already studied the refraction of light through a rectangular glass slab. In a rectangular glass slab, the emergent light rays are parallel to the incident light rays because the opposite faces of a rectangular glass slab are parallel to one another. We will now discuss the refraction of light through a glass object whose opposite faces are not parallel to one another.
In refraction through a glass slab, the emergent ray is parallel to the incident ray but in refraction through a glass prism, the emergent ray is not parallel to the incident ray.
The angle between incident ray and emergent ray is called angle of deviation.
Dispersion of Light
In the year 1665,Newton discovered by his experiments with glass prism that white light(like sunlight) consists of a mixture of seven colours. Newton found that if a beam of white light is passed through a triangular glass prism, the white light splits to form a band of seven colours on a white screen, when a beam of white light passed through a glass prism is called a spectrum of white light.
- The splitting up of white light into seven colour on passing through a transparent medium like a glass prism is called dispersion of light.
- When white light consisting of seven colour falls on a glass prism, each colour in it is reflected (or deviated) by a different angle with the resultant that seven colour are spread out to form a spectrum, red colour has the maximum speed in glass ,so the red colour is deviated the least.
The Rainbow
The rainbow is an arch of seven colour visible in the sky, which is produced by the dispersion of sun's light by raindrops in the atmosphere. Each raindrop acts as a tiny glass prism, splitting the sunlight into a spectrum.
The raindrop in the atmosphere act like many small prisms. A rainbow is always formed in a direction opposite to that of the sun.