Question
Why does a ray falling normally on a plane mirror, retrace its path?
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Answer
The ray traces its path when it falls normally on a plane mirror because the angle of incidence is equal to the angle of reflection. Explanation: According to the 'law of reflection' the angle of 'incidence' is always equals to the "angle of reflection". If a ray falls normally it means it is falling on the 'plane mirror' at right angle. So the 'angle of incidence' is 90 degrees and so is the 'angle of reflection.
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