Ray Optics and Optical Instruments - Result Question 1
1. 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 I. 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
[2017]
(a) $\frac{y}{x}$
(b) $\frac{x}{2 y}$
(c) $\frac{x}{y}$
(d) $\frac{y}{2 x}$
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Solution:
- (d) When mirror is rotated by angle $\theta$ reflected ray will be rotated by $2 \theta$.
According to the condition,
$ \frac{y}{x}=2 \theta \quad \Rightarrow \theta=\frac{y}{2 x} $
