Refractive index of a long cylinder made of transparent material is increasing as we are moving away from its axis. A beam of parallel rays, parallel to the axis of the cylinder is incident on one end of the rod as shown in figure. Then which of the following diagrams correctly shows the shape of wavefront inside the rod?

Question

Infinity Learn · Accepted Answer

Speed of light in a medium other than vacuum is given by $$V=C$$μ. As we are moving away from the axis of the rod, μ is increasing and so V is decreasing. So the light on the axis of the rod will traverse more length of path in a given interval of time than the light near its surface.

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