Physics for Scientists and Engineers: A Strategic Approach with Modern Physics (3rd Edition)

Published by Pearson
ISBN 10: 0321740904
ISBN 13: 978-0-32174-090-8

Chapter 20 - Traveling Waves - Exercises and Problems: 63

Answer

(a) $I = 0.099~W/m^2$ (b) $I = 1.6\times 10^6~W/m^2$

Work Step by Step

(a) The light from the light bulb spreads in all directions from the light bulb. We can find the light intensity on a wall 2.0 meters away. $I = \frac{P}{A}$ $I = \frac{P}{4\pi~R^2}$ $I = \frac{5.0~W}{(4\pi)(2.0~m)^2}$ $I = 0.099~W/m^2$ (b) The light from the laser does not spread out as it leaves the laser. The light stays in a beam with a diameter of 2.0 mm. We can find the light intensity on a wall 2.0 meters away. $I = \frac{P}{A}$ $I = \frac{P}{\pi~R^2}$ $I = \frac{5.0~W}{(\pi)(1.0\times 10^{-3}~m)^2}$ $I = 1.6\times 10^6~W/m^2$
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