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.

As the beam enters the medium, it will

(A)diverge
(B)converge✓ Correct
(C)diverge near the axis and converge near the periphery
(D)travel as a cylindrical beam

Answer: (B)

Solution

The refractive index

μ = μ_{0} + μ_{2} I

is largest where the intensity is largest, which is on the axis of the beam, and it falls off towards the edges. Since light travels more slowly where the index is higher, the central part of each wavefront lags behind the edges. The wavefront curves so that it bends inward, and the beam converges.

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

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

Solution

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