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504_Physics ProblemsTechnical Physics

504_Physics ProblemsTechnical Physics - 506 P17.25 Sound...

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506 Sound Waves P17.25 (a) I 1 12 10 12 80 0 10 1 00 10 10 1 00 10 10 1 = × = × . . . W m W m 2 2 e j e j b g β or I 1 4 1 00 10 = × . W m 2 I 2 12 10 12 75 0 10 1 00 10 10 1 00 10 10 2 = × = × . . . W m W m 2 2 e j e j b g β or I 2 4.5 5 1 00 10 3 16 10 = × = × . . W m W m 2 2 When both sounds are present, the total intensity is I I I = + = × + × = × 1 2 4 5 4 1 00 10 3 16 10 1 32 10 . . . W m W m W m 2 2 2 . (b) The decibel level for the combined sounds is β = × × F H G I K J = × = 10 1 32 10 1 00 10 10 1 32 10 81 2 4 12 8 log . . log . . W m W m dB 2 2 e j . *P17.26 (a) We have λ = v f and f is the same for all three waves. Since the speed is smallest in air, λ is smallest in air. It is larger by 1 493 331 4 51 m s m s times = . in water and by 5 950 331 18 0 = . times in iron . (b) From I v s = 1 2 2 2 ρ ω max ; s I v max = 2 0 0 2 ρ ω , s max is smallest in iron, larger in water by ρ ρ iron iron water water times v v = = 7 860 5 950 1 000 1 493 5 60 . , and larger in air by 7 860 5 950 1 29 331 331 = . times . (c) From I P v = max 2 2 ρ ; P I v max = 2 ρ , P max is smallest in air, larger in water by 1 000 1 493 1 29 331 59 1 = . . times , and larger in iron by
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