Question

A ray of light is incident at an angle ion one face of prism of small angle A and emerges normally from the other surface. µ is the refractive index of the material of the prism. The angle of incidence is _____________.

Options

• `"A"/(2µ)`

• Aµ

• `"A"/µ`

• `("A"µ)/2`

Answer 1

A ray of light is incident at an angle ion one face of prism of small angle A and emerges normally from the other surface. µ is the refractive index of the material of the prism. The angle of incidence is Aµ.

Explanation:

The path followed by ray of light is shown in figure

As, the ray emerges normally from other surface. So, angle of emergence is zero.

The angle of deviation i.e., between incident and emergent ray is

δ = (i + e) − A = i − A ......(i) (∵ e = 0)

Also, for minimum deviation, δ = (µ − 1)A ....(ii)

From Eqs. (i) and (ii), we get

i − A = (µ − 1)A

i = (µ − 1)A + A

= µA