An initially parallel cylindrical beam travels in a medium of refractive index `mu(l)=mu_(0)+mu_(2)l`, where `mu_(0)` and `mu_(2)` are positive constants and l is the intensity of the light beam. The intensity of the beam is decreasing with increasing radius.
The inital shape of the wave front of the beam is

Options

A. planar
B. convex
C. concave
D. convex near the axis and concave near the periphery

Answer

A

Explanation

Parallel cylinderical beam gives planar wavefront