An intially parallel cyclindrical beam travels in a medium of refractive index `mu (I) = mu_(0) + mu_(2) I`, where `mu_(0)` and `mu_(2)` are positive constants and `I` is intensity of light beam. The intensity of the beam is decreasing with increasing radius.
Answer the following questions :
The speed of light in the medium is

Options

A. maximum on the axis of the beam
B. minimum on the axis of the beam
C. the same everywhere in the beam
D. directly proportional to the intensity I

Answer

B

Explanation

`mu=(c)/(v)impliesv=(c)/(mu)`
Since I is decreasing so `mu` also decreases and hence v increases. So v is minimum on the axis of the beam.