An initially parallel cylindrical beam travels in a medium of refractive index $$\mu \left( I \right) = {\mu _0} + {\mu _2}I,$$ 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.
The initial shape of the wave front of the beam is
A.
convex
B.
concave
C.
convex near the axis and concave near the periphery
D.
planar
Answer :
planar
Solution :
Initially the parallel beam is cylindrical . Therefore, the wave front will be planar.
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