Question

An initially parallel cylindrical beam travels in a medium of refractive index $\mu \left(I\right)={\mu }_0+{\mu }_{2}I$, where ${\mu }_0$ and ${\mu }_2$ are positive constants and $I$ is the intensity of the light beam. The intensity of the beam is decreasing with increasing radius. How does beam travel after entering in medium?

• A. Diverge
• B. Converge
• C. Diverge near the axis and converge near the periphery
• D. Travel as a planar beam

Answer 1

Answer: (B)

Converge

$\begin{array}{c}\text{The beam will converge because intensity is maximum}\\ \text{at axis}\\ \therefore \text{refractive index}\mu \text{will be maximum and speed}\\ \text{will be minimum on axis of the light beam}\\ \mu \propto \frac{1}{v}\end{array}$