Question

A small plane mirror is 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 the spot of light on the screen after reflection from the mirror will be

• A. $\frac{nR}{2\pi }$
• B. $\frac{nR}{4\pi }$
• C. $2n\pi R$
• D. $4n\pi R$

Answer 1

The correct option is D

$4n\pi R$

If mirror rotates through an angle $\theta$, the reflected ray rotates through an angle 2$\theta$.

So, $V=\omega R$

$=R\times 2\pi \times 2n$

$=4\pi nR$