JEE Main · 2010 · 11 Apr 2010 · Offline · Wave Optics

Passage

An initially parallel cylindrical beam travels in a medium of refractive index

μ (I) = μ_{0} + μ_{2} I

, where

μ_{0}

and

μ_{2}

are positive constants and

I

is the intensity of the light beam. The intensity of the beam is decreasing with increasing radius.

The speed of light in the medium is

(A)minimum on the axis of the beam✓ Correct
(B)the same everywhere in the beam
(C)directly proportional to the intensity I
(D)maximum on the axis of the beam

Answer: (A)

Solution

The speed of light in the medium is

v = c / μ

with

μ = μ_{0} + μ_{2} I

. The intensity is greatest on the axis and falls off outward, so the index is greatest on the axis. A larger index means a smaller speed, so the light travels slowest on the axis, that is the speed is minimum there.

JEE Main · 2010 · 11 Apr 2010 · Offline · Single correct option

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