Physics [3 Mark Question Answer]

The splitting of white light into its constituents colours when white light passes through a prism is called dispersion of light.
The cause of dispersion is the deviation of light of different colours through different angles, by a prism.

The reason is that the speed of violet light in glass is least while that of red light is most. Since. Refractive index of glass = speed of light in air/speed of light in the glass, so the refractive index of glass (the material of prism) is most for violet light and least for the red light. Hence, the violet light has deviated most and red light is deviated least.

A spectrum in which there is the overlapping of different colours is called an impure Spectrum. In other words, in an impure spectrum, the colours are not distinct and independent but they overlap. On the other hand, a spectrum with each colour distinct and independent is called a pure spectrum.

The two electromagnetic waves and their uses having a frequency higher than that of violet light is:
X-rays: X-rays are very extensively used for medical purposes, e.g., in surgery to detect bone fractures by studying X-rays photographs.
Gamma rays: Gamma radiations are used in the cure of cancer.

The angle of deviation produced by a prism depends on the refractive index of the material of the prism. The refractive index of the material of prism is different for different colours of light because the speed of different colours is different inside the prism. Thus, the light of different colours is deviated through different angles, by a prism.

The labelled ray diagram showing the formation of the spectrum of sunlight on a screen is given below. The colour obtained nearer the base of the prism is violet.

When viewed from above – Red.
When viewed from below – Blue.
When viewed from sides – Green.