On a hot summer night,the refractive index of | vedclass

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(C) According to the problem,the refractive index $\mu$ of air increases with height from the ground. Since the speed of light $v$ in a medium is give

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bends upwards

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(C) According to the problem,the refractive index $\mu$ of air increases with height from the ground. Since the speed of light $v$ in a medium is given by $v = c/\mu$,where $c$ is the speed of light in vacuum,the speed of light $v$ decreases as the height from the ground increases. Consider a plane wavefront moving horizontally. The part of the wavefront at a greater height travels slower than the part of the wavefront closer to the ground. According to Huygens' principle,each point on the wavefront acts as a source of secondary wavelets. Because the lower part of the wavefront travels faster,the wavefront tilts,causing the direction of propagation (which is perpendicular to the wavefront) to bend upwards. Therefore,the light beam bends upwards.

On a hot summer night,the refractive index of air is smallest near the ground and increases with height from the ground. When a light beam is directed horizontally,the Huygens' principle leads us to conclude that as it travels,the light beam

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