An initially parallel cylindrical 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 $\mathrm{I}$ 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

• Correct answer
  A

  minimum on the axis of the beam
• B

  the same everywhere in the beam
• C

  directly proportional to the intensity I
• D

  maximum on the axis of the beam

Hence, the correct answer is option: 'A'.