Question

A short pulse of white light is incident from air to a glass slab at normal incidence. After travelling through the slab, the first colour to emerge is ______.

Options

• blue

• green

• violent

• red

Answer 1

A short pulse of white light is incident from air to a glass slab at normal incidence. After travelling through the slab, the first colour to emerge is red.

Explanation:

As velocity of wave is given by the relation `v = f λ`. When light ray goes from one medium to other medium, the frequency of light remains unchanged. Hence `v  oo  λ` or greater the wavelength, greater the speed.

The light of red colour is of the highest wavelength and therefore of the highest speed. Therefore, after travelling through the slab, the red colour emerges first.