The Obedient Reflected Ray

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Two mirrors are joined at a fixed angle at . A ray of light shines into the angle between them, parallel to the horizontal mirror and at a given height. It bounces a number of times. Suppose it strikes the lower mirror at right angles at and then reemerges along the original path. This is called an obedient ray.


What is the relationship between the distance between the height and the length of ? The answer is given in the Details.


Contributed by: Izidor Hafner (December 2015)
Open content licensed under CC BY-NC-SA



They are equal.


[1] D. Wells, The Penguin Book of Curious and Interesting Puzzles, New York: Penguin Books, 1992.

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