MCAT Question A Day - 9/12/13 - Answer!
What is the intensity, in W/m2, of sound with a sound level of 20 dB?
A. 10-12 W/m2
B. 10-10 W/m2
C. 1 W/m2
D. 10 W/m2
The correct answer is (B). b = 10 log I/I0. The threshold of hearing is 0 dB = 10-12 W/m2. Since each 10 dB represents an order of magnitude of intensity, 20 dB is two orders of magnitude (100x) greater than the threshold intensity. This gives it an intensity of 10-10 W/m2.
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