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HW #8-solutions

# HW #8-solutions - nanni(arn437 HW#8 Erskine(56905 1 This...

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nanni (arn437) – HW #8 – Erskine – (56905) 1 This print-out should have 21 questions. Multiple-choice questions may continue on the next column or page – find all choices before answering. 001(part1of2)10.0points The output of a generator is given by V = V max sin ω t . If after 0 . 0134 s , the output is 0 . 25 times V max , what is the largest possible angular velocity of the generator? Correct answer: 18 . 8567 rad / s. Explanation: Let : V = 0 . 25 V max , and t 1 = 0 . 0134 s . (0 . 25) V max = V max sin( ω t 1 ) ω t 1 = sin 1 (0 . 25) . So the largest possible angular velocity is ω = sin 1 (0 . 25) t 1 = sin 1 (0 . 25) 0 . 0134 s = 18 . 8567 rad / s , since there are an infinite number of higher harmonics. 002(part2of2)10.0points What is the next time (value of t ) for which the output is 0 . 25 times V max ? Correct answer: 0 . 153203 s. Explanation: θ V max 0 t 1 t 2 t 1 T 2 From the figure, we see that the next value of t for which V = (0 . 25) V max occurs at t 2 = T 2 - t 1 , where T is the period. The frequency is given by f = ω 2 π , and the period by T = 1 f = 2 π ω , so the required time is t 2 = T 2 - t 1 = π ω - t 1 = π 18 . 8567 rad / s - 0 . 0134 s = 0 . 153203 s . Note: The third time for which the output is 0 . 25 times V max is simply t 3 = t 1 + T , where T is the period. 003 10.0points The graph below depicts an oscillating emf . E max E min 0 φ 0 T/ 2 T Which phasor diagram correctly represents this oscillation? Assume counter-clockwise rotation. 1. E φ 2. E φ

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nanni (arn437) – HW #8 – Erskine – (56905) 2 3. E φ 4. E φ 5. E φ correct Explanation: The oscillating emf is proportional to sin( ωt - φ ). So the right answer is E φ 004(part1of3)10.0points An AC voltage of the form V = V max sin 2 πft , with frequency 72 Hz and maximum voltage 872 V, is applied across a 51 W light bulb. When the voltage is first applied, what is the current through the circuit? 1. the rms current 2. 0 correct 3. the maximum current Explanation: Let : t = 0 . The current in the circuit is I = I max sin(2 π f t ) = I max sin 0) = 0 .
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HW #8-solutions - nanni(arn437 HW#8 Erskine(56905 1 This...

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