Shown in the figure are two plane mirrors XY and YZ (XY \perp YZ) joined at their edge. Also shown is a light ray falling on one of the mirrors and reflected back parallel to its original path as a result of this arrangement. The two mirrors are now rotated by an angle \theta to their new position X'YZ', as shown. As a result the new reflected ray is at an angle \alpha from the original reflected ray. Then :
- A. \alpha=0 ✓
- B. \alpha=\theta
- C. \alpha=2\theta
- D. \alpha=4\theta
Correct Answer: A. \alpha=0
Explanation
When two mirrors are perpendicular, the final reflected ray is always anti-parallel to the incident ray, irrespective of the angle of incidence. Rotating the whole system does not change this relative alignment, so the angle \alpha between the original and new reflected ray is 0.
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