Question

The initial shape of the wavefront of the beam is

An initially parallel cylindrical beam travels in a medium of refractive index μ(I) = μ₀ + μ₂I, where μ₀ and μ₂ are positive constants and I is the intensity of the light beam. The intensity of the beam is decreasing with increasing radius.

(a) planar 

(b) convex

(c) concave

(d) convex near the axis and concave near the periphery

Answer 1

(a) : As the beam is initially parallel, the shape of wavefront is planar.