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exam04_F08-white-solutions - Exam 4 – white version...

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Unformatted text preview: Exam 4 – white version Physics 2760 FS 2008 Last Name______________________________ First Name_____________________________ ID # ___________________ This is a closed book exam. I understand, pursuant to University Regulations on academic honesty, that I am not to use any notes or information other than what is in the official, non‐annotated formula sheet. Signature_______________________________________ For multiple choice questions, please make sure that you circle the letter for the answer which you believe to be correct and only that answer. If more than one answer is circled for the same problem, you will not receive credit for it. Don’t get hung up on questions. They should take only one or two minutes each. If you find yourself spending more than a few minutes on a multiple choice question you are probably looking at it the wrong way. You should skip it for now and come back to it later. For full credit show your work for solutions to questions that require calculations. Explain from where you start to solve the problem and show your math flowing from it for full credit. No shown work, no credit! Relax, read carefully, think – and then read everything again. During the exam, if you have questions please raise your hand and the TA or the instructor will come to you and provide help. 6. (5 points) In the figure below, which of the phasor diagrams represents a series R‐L‐C circuit driven at resonance? 7. An L‐C circuit consists of an inductor with an inductance of 90 mH and a capacitor with a capacitance of 400 μF. The initial charge on the capacitor is + 6.0 μC (on the top plate), and the initial current in the inductor is zero. a) (3 points) Calculate the angular frequency of the circuit. b) (3 points) What is the maximum current? c) (3 points) At what time is the current maximum for the first time? d) (5 points) What is the emf through the inductor at that time (when current is maximum)? e) (5 points) At what time does the top plate of the capacitor become negative for the first time? f) (5 points) At what time is the current in the inductor half its maximum value? 8. A series RLC circuit consists of a 50 Ω resistor, a 3 mH inductor, and a 480 nF capacitor. It is connected to a 5000 Hz generator with a voltage amplitude of 5 V. Surround your answers with a box. a) (6 points) Find the capacitive reactance XC, inductive reactance XL, and impedance Z. b) (4 points) Find the current amplitude, and the phase angle. c) (8 points) What is the voltage across the capacitor at time t = 0.001 s? First write the algebraic expression you will use to calculate the voltage and then substitute numbers. d) (8 points) Draw a phasor diagram for this circuit, clearly indicating each phasor and angle. 9. In the figure below, switch S1 is closed while switch S2 is kept open. The inductance is L = 0.160 H, and the resistance is R = 125 Ω. When the current has reached its final value, the energy stored in the inductor is UL = 0.32 J. a) (4 points) What is the maximum value of the current? b) (4 points) What is the emf of the battery? c) (7 points) After the current has reached its final value, S1 is opened and S2 is closed. How much time does it take for the energy stored in the inductor to decrease to a half of the original value? MC 35/ Q7 24/ Q8 26/ Q9 15/ Total 100/ ...
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