An e.m. wave is travelling through a medium of refractive index `mu_1`, and is incident on the boundary of a medium of refractive index `mu_2`. IF the wave reflects at the boundary

Options

A. The wave undergoes a phase change of `180^@` if `mu_1 lt mu_2`
B. The wave undergoes a phase change of `180^@` if `mu_1 gt mu_2`
C. The wave undergoes a phase change if `mu_1 lt mu_2`
D. The wave undergoes a phase change if `mu_1 gt mu_2`

Answer

(a,d)

Explanation

Note than an e.m. wave undergoes a
phase change of `180^@` on reflection. From a denser
medium, i.e., a medium that has a larger refractive
index than one in which it is travelling. However,
there is no phase reversal if the case is opposite.