A small plane mirror placed at the centre of a spherical screen of radius R. A beam of light is falling on the mirror. If the mirror makes n revolution. per second, the speed of light on the screen after reflection from the mirror will be

4ΠnR

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2ΠnR

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Solution

The correct option is A 4ΠnR
When plane mirror rotates through an angle θ, the reflected ray rotates through an angle 2θ. So spot on the screen will make 2n revolution per second.

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