question_answer

A beam of light from a source 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 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              

A) \[\frac{x}{y}\]                                   

B) \[\frac{y}{2x}\]

C) \[\frac{y}{x}\]                                   

D)   \[\frac{x}{2y}\]

Correct Answer: B

Solution :

                 When mirror is rotated by\[\theta \]angle reflected ray will be rotated by\[2\theta .\] \[\frac{y}{x}=2\theta \] \[\theta =\frac{y}{2x}\]