Question

According to Stoke’s law, the phase change of ____ takes place when light in denser medium reflects from rarer medium (a) 0 (b) π/4 (c) π (d) π/2​

Answer 1

Explanation:

I think answers will be π/2

Answer 2

Answer:

According to Stoke’s law, the phase change of π takes place when the light in a denser medium reflects from rarer medium i.e.option (c)

Explanation:

Let's consider two rays of amplitude ar₁² and at₁t₂.

According to the principle of optical reversibility, the two rays of amplitudes ar₁² (in rarer) and at₁t₂ (in a denser medium) must combine to give the incident ray.

So,

ar₁²+at₁t₂=a

t₁t₂=1-r₁²          (1)                      (stokes relation)

And other two rays of amplitude at₁r₁ (in a denser medium) and at₁r₂ (rays coming back to denser medium) must cancel each other.

So,

at₁r₁ + at₁r₂=0

r₂=-r₁                (2)                   (stokes relation)

Equation (1) and (2) shows that there is the reversal of phase when the ray of light is reflected by a denser medium and there is no absorption of light.

The -ve sign in the amplitude of the reflected wave indicates the phase difference of π between two rays.

Hence, according to Stoke’s law, the phase change of π takes place when the light in a denser medium reflects from rarer medium i.e.option (c)