Question

A beam of light from a sources L is incident normally on a plane mirror fixed at a certain distance x from the source. the beam is reflected back as a spot on a scale placed just above the source L. When the mirror is rotated through s small angle $\Theta$, the mirror is rotated through a small angle $\Theta$, the spot of the light is found to move through a distance y on the scale. The angle $\Theta$ is given by

Answer 1

when the mirror is rotated by $\theta$ angle reflected ray will be rotated by $2\theta$

$\therefore$ $\frac{y}{x}=2\theta$

$\theta =\frac{y}{2x}$