Question

Why do we observe seven colours when white light passes through prism?

Answer 1

Hey Friend,

When a white light is incident on the principle section of the prism, a band of seven colours was observed in the order, resembling the rainbow formed after the rain!

This occurs due to a phenomenon known as Dispersion.
Dispersion :- The phenomenon due to which a polychromatic light (white light) splits into component colours, when passed through a prism is called Dispersion.
The order of colours from base of prism - Violet, Indigo, Blue, Green, Yellow, Orange, Red. 
You can remember this sequence as VIBGYOR!!!

Now, we know that angle of deviation for different wavelengths or colours is different.
Re-frangibility :- The angle through which light of particular wavelength can deviate while passing through a prism is called Re-frangibility!
In the spectrum (band of seven colours)... the re-frangibility of red light is the least whereas the re-frangibility for violet light is maximum.

Thus, the white light separates or disperses into different colours according to its angle of deviation of Re-frangibilty.
This happens on one surface (while entering the prism)...but when passing from the another surface (while getting out from the prism)...there is simple refraction of light!
And therefore, we observe seven different colours on the screen which is commonly called spectrum!

The following diagram will help you understand it better...

Hope it helps!

Answer 2

Answer:

When light passes through a prism it offers different refractive indices to the different 1 wavelengths of light. Thus, each colour suffers a different deviation. The red light deviates the least

Explanation:

hope it helps you