506_Physics ProblemsTechnical Physics

506_Physics ProblemsTechnical Physics - 508 P17.30 Sound...

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508 Sound Waves P17.30 Let r 1 and r 2 be the distance from the speaker to the observer that hears 60.0 dB and 80.0 dB, respectively. Use the result of problem 28, ββ 21 1 2 20 −= F H G I K J log r r , to obtain 80 0 60 0 20 1 2 .. l o g F H G I K J r r . Thus, log r r 1 2 1 F H G I K J = , so rr 12 10 0 = . . Also: 110 += m, so 10 0 110 22 . m giving r 2 10 0 = . m , and r 1 100 = m. P17.31 We presume the speakers broadcast equally in all directions. (a) r AC =+ = 300 400 500 . m m I r = = × = × F H G I K J == 4 100 10 45 0 0 318 10 10 10 10 6 50 65 0 2 3 2 6 6 12 π β . . . log . W m Wm dB dB dB 2 2 2 af (b) r BC = 447 . m I = × = × F H G I K J = 150 10 44 4 7 597 10 10 10 67 8 3 2 6 6 12 . . . log . . W m dB dB 2 a f (c) I 318 597 µµ = × F H G I K J = 10 915 10 10 69 6 6 12 dB dB log . . P17.32 In I r = 4 2 , intensity I is proportional to
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