Q. 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) $\frac{y}{2x}$
B) $\frac{y}{x}$
C) $\frac{x}{2y}$
D) $\frac{x}{y}$
Explanation
[Solution] Rotating the mirror by $\theta$ turns the reflected ray by $2\theta$, so $y = 2\theta x$ and $\theta = y/(2x)$. Answer (1).
Reviewed by Dr. Abubacker
Physics Educator & NEET/JEE Specialist
Ph.D. in Physics with 19+ years of teaching experience.