502_Physics ProblemsTechnical Physics

502_Physics ProblemsTechnical Physics - 504 Sound Waves...

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504 Sound Waves Section 17.3 Intensity of Periodic Sound Waves *P17.18 The sound power incident on the eardrum is ℘= IA where I is the intensity of the sound and A 50 10 5 . m 2 is the area of the eardrum. (a) At the threshold of hearing, I 10 10 12 W m 2 , and × × = × −− 1 0 10 5 0 10 5 00 10 12 5 17 .. . Wm m W 22 ej e j . (b) At the threshold of pain, I = 10 . Wm 2 , and × = × 500 10 55 . m W e j . P17.19 β = F H G I K J = × × F H G I K J = 10 10 400 10 100 10 66 0 0 6 12 log log . . . I I dB P17.20 (a) 70 0 10 12 .l o g . dB 2 = × F H G I K J I Therefore, I = × 1 00 10 10 1 00 10 12 70 0 10 5 . bg . (b) I P v = max 2 2 ρ , so Pv I P max max . == × = 1 2 0 3 4 3 1 0 0 1 0 90 7 5 kg m m s W m mPa 32 P17.21 Is v = 1 2 ρω max (a) At f = 2 500 Hz , the frequency is increased by a factor of 2.50, so the intensity (at constant s max ) increases by 2 50 6 25 2 af = . Therefore,
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