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

Options

A. `4 pi n R `
B. `2 pi n R `
C. `(nR )/(2pi )`
D. `( nR )/( 4 pi)`

Answer

A

Explanation

When plane mirror rotates through an angle `theta` , the reflected ray rotates by an angle `2 theta`.
Hence, spot on the screen will make 2n revolution per second. i.e. (2`pi` R)2n = 4`pi` n R.