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HW 32 - terry(ect328 homework 32 Turner(59130 This...

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terry (ect328) – homework 32 – Turner – (59130) 1 This print-out should have 10 questions. Multiple-choice questions may continue on the next column or page – find all choices before answering. 001 (part 1 of 3) 10.0 points In an LR circuit, a 174 V( rms ), 78 Hz source is in series with a 21 mH inductor and a 10 Ω resistor. What is the maximum rms current? Correct answer: 12 . 1254 A. Explanation: Let : f = 78 Hz , L = 0 . 021 H , R = 10 Ω , and V rms = 174 V . The inductive reactance is X L = ω L = 2 π f L = 2 π (78 Hz) (0 . 021 H) = 10 . 2919 Ω . The impedance of an RL circuit is the same as that of an RLC circuit, but without the capacitive reactance. Namely Z = R 2 + X 2 L = (10 Ω ) 2 + (10 . 2919 Ω ) 2 = 14 . 35 Ω . The rms current is I rms = V rms Z = 174 V 14 . 35 Ω = 12 . 1254 A . 002 (part 2 of 3) 10.0 points What is the power factor? Correct answer: 0 . 696864. Explanation: The phase angle in an RL circuit is the same as that of an RLC circuit, but without the capacitive reactance. Namely φ = tan - 1 X L R = tan - 1 10 . 2919 Ω 10 Ω = 45 . 824 So, the power factor is cos φ = cos(45 . 824 ) = 0 . 696864 .
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