The phase change in reflected wave, when light wave suffers reflection at the interface from air to glass is

(A) $0$

(B) $\dfrac{\pi }{2}$

(C) $\pi $

(D) $2\pi $

Hint: A phase change occurs when a wave is reflected and for light waves it occurs only when reflection is taking place at a surface of higher refractive index than the medium it is travelling in.

Complete step-by-step solution
When light waves are passing from one medium to another the phase associated with the wave also changes. But phase change does not occur for every reflection. In light waves a phase change of 180o takes place when they reflect from the surface whose refractive index of the medium is higher than the medium they are travelling.








A light wave undergoes a phase change by π when travelling in air suffers reflection at glass but no phase change occurs when it is moving in glass and gets reflected at the surface of air.

Hence, the correct option is C.

Note: This is the reason why the optical boundaries are in ordered pairs mentioned as glass-air suggesting from which material the light is moving out and into. This phase change also plays an important role in thin film interference.