Question

Differentiate between a glass slab and a glass prism. What happens when a narrow beam of (i) a monochromatic light, and (ii) white light passes through (a) glass slab and (b) glass prism?

Answer 1

Hint: Refraction occurs when light passes through a glass slab or a glass prism.
 The glass prism disperse white light, whereas glass slab doesn’t.

Complete step by step answer:
A glass slab is a rectangular, transparent medium, bounded by four surfaces. The two parallel, horizontal surfaces act as the refracting surface.
A glass prism is a homogenous, transparent medium bounded by two plane surfaces, inclined to each other at an angle. The two surfaces are called refracting surfaces and the angle between them is called the angle of the prism.
When monochromatic light passes through a glass slab, it suffers refraction at the first surface, whereas at the second surface, it suffers both reflection and refraction, and the reflected ray again suffers refraction at the first surface emerging out in the air.
However when white light passes through a glass slab, it suffers refraction at the first surface, and splits into its component colored rays. At the second surface these colored rays suffer reflection and are reversed back to the first surface, undoing the effect of the first surface. At the surface the light again suffers refraction and emerges out as white light.

When monochromatic light passes through a glass prism, the light suffers double refraction, one at refracting surface at which it is incident at and the second at the opposite the refracting surface through which it emerges out in the air.
When white light falls on a glass prism, it splits into the rays of its constituent colors. The reason for ‘dispersion’ of light is that in glass the light rays of different colors travel with different speed, although in vacuum rays if all colors travel with the same speed. The emergent rays are of different colors. The ray of red light bends minimum towards the base of the prism, while violet light bends maximum.

Note:
The glass slab acts as a plane mirror forming multiple distinguished images, if light is coming through an object. Both glass slab and glass prism refract light because the speed of light changes on passing from one medium to another.