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Unformatted text preview: thwing (jrt2329) Homework 10 Yao (59110) 1 This printout should have 25 questions. Multiplechoice questions may continue on the next column or page find all choices before answering. 001 (part 1 of 2) 10.0 points An AC voltage of rms value 515 V and fre quency 15 Hz is connected across a light bulb with a resistance of 280 . What is the rms current? Correct answer: 1 . 83929 A. Explanation: Let : V rms = 515 V and R = 280 . The rms current is I rms = V rms R = 515 V 280 = 1 . 83929 A . 002 (part 2 of 2) 10.0 points What is the maximum current? Correct answer: 2 . 60114 A. Explanation: The maximum current is I max = 2 I rms = 2(1 . 83929 A) = 2 . 60114 A . 003 10.0 points A lightbulb is connected to a 60 Hz power source having a maximum voltage of 167 V. What is the resistance of the light bulb that uses an average power of 57 . 5 W? Correct answer: 242 . 513 . Explanation: Let : V max = 167 V and P av = 57 . 5 W . The rms voltage is V rms = V max 2 = 167 V 2 = 118 . 087 V . The average power is P av = V 2 rms R R = V 2 rms P av = V 2 max 2 P av = (167 V) 2 2 (57 . 5 W) = 242 . 513 . 004 (part 1 of 2) 10.0 points What maximum current is delivered to a 2 . 07 F capacitor when connected across a North American outlet having rms voltage 120 V and frequency 60 Hz? Correct answer: 132 . 433 mA. Explanation: Let : C = 2 . 07 F = 2 . 07 10 6 F , V rms = 120 V , and f = 60 Hz . The rms current is I rms = V rms X C = V rms 2 f C , so the maximum current is I max = 2 I rms = 2 2 V rms f C = 2 2 (120 V) (60 Hz) (2 . 07 10 6 F) 10 3 mA A = 132 . 433 mA . 005 (part 2 of 2) 10.0 points For the same capacitor, calculate the max imum current for a European outlet having rms voltage 240 V and frequency 50 Hz. Correct answer: 220 . 722 mA. thwing (jrt2329) Homework 10 Yao (59110) 2 Explanation: Let : V rms = 240 V and f = 50 Hz . The maximum current is I max = 2 2 V rms f C = 2 2(240 V) (50 Hz) (2 . 07 10 6 F) 10 3 mA A = 220 . 722 mA . 006 10.0 points A circuit containing resistance only is con nected to a 110V, 60Hz line. If a capacitor is connected in series with the resistance, how will the current change? 1. The current lags the emf . 2. The current is decreased. correct 3. The current is in phase with the emf . 4. The current is increased. 5. The current remains the same. Explanation: In an AC circuit containing only capaci tance and resistance, the current leads the voltage by 90 . For a capacitor in an AC circuit, its resistance X C = 1 2 f C is not equal to 0. So if you connect a capacitor with the resistance in series, the resistance will increase, and the current will decrease....
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This note was uploaded on 11/11/2009 for the course PHY 59110 taught by Professor Yao during the Spring '09 term at University of Texas at Austin.
 Spring '09
 YAO
 Physics, Work

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