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Physics 302L shih test 2

# Physics 302L shih test 2 - Version 060 Exam2 shih(56310...

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Version 060 – Exam2 – shih – (56310) 1 This print-out should have 12 questions. Multiple-choice questions may continue on the next column or page – find all choices before answering. 001 10.0points Consider a long straight wire and a wire loop in the same plane. The long wire has a current flowing in the direction shown. The wire loop is moving in the direction shown. I v wire loop wire straight The current in the loop is flowing 1. counter-clockwise. 2. clockwise. correct 3. There is no current in the loop. Explanation: Using the right hand rule, and taking into consideration the direction of the magnetic field, we find that the direction of the current flowing in the loop is as shown in the figure. × × × × × × × × × I v i B 002 10.0points Calculate the resonance frequency of a se- ries RLC circuit for which the capacitance is 26 μ F , the resistance is 54 kΩ , and the induc- tance is 138 mH . 1. 56.841 2. 133.185 3. 67.5941 4. 114.326 5. 59.9157 6. 84.0222 7. 82.2531 8. 46.1367 9. 43.5331 10. 58.914 Correct answer: 84 . 0222 Hz. Explanation: Let : R = 54 kΩ = 54000 Ω , L = 138 mH = 0 . 138 H , and C = 26 μ F = 2 . 6 × 10 - 5 F . The resonance frequency is the frequency at which the current becomes maximum, or the impedance becomes minimum. This occurs when X L = X C ω L = 1 ω C . From this condition, the resonance frequency is given by f = 1 2 π L C = 1 2 π radicalbig (0 . 138 H) (2 . 6 × 10 - 5 F) = 84 . 0222 Hz . 003 10.0points In the circuit below, initially the switch S 1 is in position “a” and switch S 2 is closed. L R C 2 C 1 E S 1 b a S 2

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Version 060 – Exam2 – shih – (56310) 2 When the switch S 1 is then thrown to “b”, the voltage will oscillate at a frequency which is 1. zero, since the circuit was not oscillating to begin with. 2. the same whether switch S 2 is open or closed. 3. lower when switch S 2 is open. 4. zero, since the battery is no longer in the circuit. 5. higher when switch S 2 is open. correct Explanation: The oscillation frequency is ω = 1 L C = 1 radicalbig L ( C 1 + C 2 ) . The capacitors are parallel C = C 1 + C 2 , thus when switch S 2 is opened the capacitance decreases and its inverse increases. Therefore, the frequency ω is higher when only ONE of the capacitors is connected.
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