A beam of light from a source L is incident normally upon 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 θ, the spot shifts through a distance y along the scale. The angle θ is given by:
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Question

A beam of light from a source L is incident normally upon 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 θ, the spot shifts through a distance y along the scale. The angle θ is given by:

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G1 Physics · Accepted Answer

Step 1: A mirror rotated by θ turns the reflected ray through 2θ. Step 2: For a scale at distance x from mirror, tan(2θ) = y/x. Step 3: For small θ (radians), 2θ ≈ y/x. Therefore θ ≈ y/(2x). Final answer: (A) y/(2x). Check option lettering against original, since the printed options may appear in a different order.