hw18 - Physics 21 Fall, 2004 Solution to HW-18 31 P 26 An...

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Unformatted text preview: Physics 21 Fall, 2004 Solution to HW-18 31 P 26 An LRC circuit has L = 4 . 15 mH and R = 220 . (a) What value must C have to produce resonance at 33.0 kHz? (b) What will be the maximum current at resonance if the peak external voltage is 136 V? Resonance occurs when 2 = 1 /LC , so C = 1 2 L = 1 (33 , 000 2 ) 2 ( . 00415) = 5 . 60 nF At resonance I rms = V rms q R 2 + ( L 1 /C ) 2 = V rms R = 136 220 = 0 . 618 . 31 P 40 (a) What is the rms current in an RC circuit if R = 8 . 80 k, C = 1 . 80 F, and the rms applied voltage is 120 V at 60.0 Hz? (b) What is the phase angle between voltage and current? (c) What is the power dissipated by the circuit? (d) What are the voltmeter readings across R and C ? I / C I R V Substituting numbers, we find I R = 8800 I , and I /C = 1474 I o , so V = p 8800 2 + 1474 2 I = 8923 I I = V / 8923 = 120 / 8923 = 13 . 4 mA = tan 1 1474 8800 = 9 . 51 P = I 2 R = ( . 0134) 2 8800 = 1 . 59 W V R = 8800...
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