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JEE Main 2010 (AIEEE) · Wave Theory, Wavefronts & Doppler Effect

Wave Theory, Wavefronts & Doppler Effect question from JEE Main 2010 (AIEEE)

Q23JEE Main 2010 · AIEEEDifficult

Wave Theory, Wavefronts & Doppler Effect

An initially parallel cylindrical beam travels in a medium of refractive index μ(I)=μ0+μ2I,\mu(I) = \mu_0 + \mu_2 I, where μ0\mu_0 and μ2\mu_2 are positive constants and II is the intensity of the light beam. The intensity of the beam is decreasing with increasing radius.

The initial shape of the wavefront of the beam is

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Answer: (d)

  1. The beam is initially parallel, i.e. all rays are parallel to the axis.
  2. Rays are normal to the wavefront, so parallel rays mean a plane wavefront.
  3. The intensity-dependent μ\mu changes the shape only later as the beam travels.
  4. So the answer is (d) planar.
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