Conceptual Physics (12th Edition)

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

Chapter 20 - Think and Explain: 66

Answer

The sound intensity decreases by a factor of 9.

Work Step by Step

The inverse-square law predicts that the intensity would be $\frac{1}{9}$ its original value if the distance to the source were tripled. The outgoing sound power is distributed over the surface of a sphere with 9 times the area of the original sphere, so the received power per unit area (intensity) is one-ninth of its previous value.
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