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"Answer This" Questions

Chapter 5

5-A. I ntensity versus distance

Suppose you hear a firecracker go off 60 feet away from you. The intensity you hear is 0.09 Watts/m2. What intensity would a person who is standing 20 feet away hear?
a) 0.81 Watts/m2
b) 0.27 Watts/m2
c) 0.09 Watts/m2
d) 0.03 Watts/m2
e) 0.01 Watts/m2



The intensity changes as the square of the distance. Thus, if the distance is three times closer, as it is here (60/20 = 3), the intensity is 32 = 9 times as much. Since 0.09x9=0.81 W/m2, the answer is a).

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© William J. Mullin