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Unformatted text preview: terry (ect328) oldmidterm 04 Turner (59130) 1 This printout should have 18 questions. Multiplechoice questions may continue on the next column or page find all choices before answering. 001 10.0 points In a series RLC AC circuit, the resistance is 23 , the inductance is 37 mH, and the capac itance is 22 F. The maximum potential is 119 V, and the angular frequency is 100 rad / s. Calculate the maximum current in the cir cuit. Correct answer: 0 . 263606 A. Explanation: Let : R = 23 , L = 37 mH = 0 . 037 H , C = 22 F = 2 . 2 10 5 F , V max = 119 V , and = 100 rad / s . The capacitive reactance is X C = 1 C = 1 (100 rad / s) (2 . 2 10 5 F) = 454 . 545 and the inductive reactance is X L = L = (100 rad / s) (0 . 037 H) = 3 . 7 , so the maximum current is I max = V max Z = V max radicalbig R 2 + ( X L X C ) 2 = 119 V radicalbig (23 ) 2 + (3 . 7 454 . 545 ) 2 = . 263606 A . 002 10.0 points A certain capacitor in a circuit has a capaci tive reactance of 32 . 8 when the frequency is 103 Hz. What capacitive reactance does the capac itor have at a frequency of 4880 Hz? Correct answer: 0 . 692295 . Explanation: Let : X C = 32 . 8 , f low = 103 Hz , and f high = 4880 Hz . The capacitive reactance is X C = C 2 f , so X C ( high ) X C ( low ) = 2 f low C 2 f high C = f low f high . Thus X C ( high ) = X C ( low ) f low f high = (32 . 8 ) parenleftbigg 103 Hz 4880 Hz parenrightbigg = . 692295 . 003 10.0 points A 90 mH inductor is connected to a outlet where the rms voltage is 138 V and the fre quency is 43 Hz. Determine the energy stored in the inductor at t = 5 . 4 ms, assuming that this energy is zero at t = 0. Correct answer: 2 . 8627 J. Explanation: Let : t = 5 . 4 ms = 0 . 0054 s , f = 43 Hz , L = 90 mH = 0 . 09 H , and V rms = 138 V . The inductive reactance is X L = L = 2 f L and the maximum current is I max = 2 V rms X L = 2 V rms 2 f L terry (ect328) oldmidterm 04 Turner (59130) 2 The current at time t is I = I max sin( t ) = 2 V rms 2 f L sin(2 f t ) = 2 (138 V) 2 (43 Hz) (0 . 09 H) sin[(2 (43 Hz) (0 . 0054 s)] = 7 . 97593 A , so the potential energy stored in the inductor is U = 1 2 LI 2 = 1 2 (0 . 09 H) (7 . 97593 A) 2 = 2 . 8627 J . 004 10.0 points A ideal transformer shown in the figure below having a primary with 15 turns and secondary with 12 turns. The load resistor is 53 . The source voltage is 110 V rms . 110V rms 15turns 12turns 53 What is the rms electric potential across the 53 load resistor?...
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 Fall '09
 Turner

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