512_Physics ProblemsTechnical Physics

512_Physics ProblemsTechnical Physics - 514 Sound Waves...

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514 Sound Waves Section 17.5 Digital Sound Recording Section 17.6 Motion Picture Sound *P17.48 For a 40-dB sound, 40 10 10 10 2 2 2120 343 10 287 10 12 8 2 83 dB dB ±Wm Wm kg m m s W m N m 2 2 22 2 = L N M M O Q P P == = × −− log .. max max I I P v Pv I ρ ej bg (a) code = × = 28 7 65 536 7 3 . . Nm 2 2 (b) For sounds of 40 dB or softer, too few digital words are available to represent the wave form with good fidelity. (c) In a sound wave P is negative half of the time but this coding scheme has no words available for negative pressure variations. *P17.49 If the source is to the left at angle θ from the direction you are facing, the sound must travel an extra distance d sin to reach your right ear as shown, where d is the distance between your ears. The delay time is t in v d t = sin . Then × sin sin . 11 6 343 210 10 22 3 vt d ms s 0.19 m left of center . ear ear FIG. P17.49 *P17.50 103 10 10 12 dB dB 2 = L N M M O Q P P log I (a) I r = = 200 10
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