University Physics with Modern Physics (14th Edition)

Published by Pearson
ISBN 10: 0321973615
ISBN 13: 978-0-32197-361-0

Chapter 32 - Electromagnetic Waves - Problems - Discussion Questions - Page 1072: Q32.12

Answer

The average pressure is $\frac{p}{8}$.

Work Step by Step

Because the second surface is twice as far away as the first surface, the intensity there is reduced by a factor of 4, due to the inverse square law. Equations 32.32 and 32.33 show that the pressure is proportional to the wave intensity. Furthermore, because the second surface is perfectly absorbing instead of perfectly reflecting as the first surface is, the pressure there is reduced by another factor of two, as shown by equations 32.32 and 32.33. The net result is a reduction in pressure by a factor of 8.
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