Conceptual Physics (12th Edition)

Published by Addison-Wesley
ISBN 10: 0321909100
ISBN 13: 978-0-32190-910-7

Chapter 28 - Think and Discuss: 100

Answer

In principle, you should aim your red laser just below where you see the blue fish.

Work Step by Step

Blue/violet light travels more slowly in water, compared to red light. This means that the blue light will refract and bend slightly more than red light will. So, in principle, a red laser fired back along the line of sight would not bend as much toward the normal/vertical, and it pass above the fish. So you should aim slightly below where you see the fish (though in practice, due to instrumental limitations, the difference is essentially negligible) .
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