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Unformatted text preview: Physics 21 Fall, 2004 Practice Exam #2 This exam is closed notes and closed book. You must show enough work on all problems to convince the grader you understand how to solve the problem. You may use a calculator. An equation sheet is on the last page. There are five problems; each counts 20 points. Problem 1. For the following circuit: R L C V rms ( frequency ω ) (a) Write the loop equation for this circuit. (b) If R = 20 Ω, L = 0 . 025 H, and C = 50 µ F (50 × 10 − 6 F), find the frequency ω for which the cur- rent lags the voltage across the inductor by 30 ◦ . Hint: Make sure ω > . (c) If V rms = 100 V, what is the rms current? What is the peak current? Problem 2. A magnetic field B = 0 . 2 T points out of the paper. The 10 Ω resistor moves to the left with a speed of 6 m/s, and the 20 Ω resistor moves to the right at 6 m/s. The top and bottom wires have no resistance, and the loop is 0.2 m high. 10 Ω 20 Ω B = 0.2 T (out) 6 m/s 6 m/s 0.2 m (a) What is the current induced in the circuit? (b) What direction does it ﬂow in? Problem 3. Two identical speakers driven at frequency ω are separated by a distance L = 3 . 0 m. When a mi- crophone in centered between the speakers a distance...
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