An initially parallel cylindrical beam travels in a medium of refractive index `mu(I)=mu_0+mu_2I`, where `mu_0` and `mu_2` are positive constants and I is the intensity of the light beam. The intensity of the beam is decreasing with increasing radius.
31. The initial shape of the wavefront of the beam is

Options

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

Answer

A