Question

Assertion : A beam of white light shows no dispersion on emerging from a glass slab.
Reason: Dispersion in a glass slab is zero.

• A. If both assertion and reason are true and reason is the correct explanation of assertion
• B. If both assertion and reason are true but reason is not the correct explanation of assertion
• C. If assertion is true but reason is false
• D. If both assertion and reason are false

Answer 1

Answer: (C)

Velocity of light is different for different mediums. On entering the glass slab, the constituents colours of white light undergo different amount of deviation. Thus there is dispersion inside the glass slab. After refraction at the two parallel faces of the glass slab, a ray of light emerges in a direction parallel to the direction of incidence of white light on the slab, but is laterally displaced. The beam of light has several rays, each of which is dispersed by the glass slab. These rays combine again and form white light and emerges out as white light.