Final_1Bb_w_solutions - Department of Physics UCSD Winter...

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Unformatted text preview: Department of Physics, UCSD Winter 2009 – Physics 1B(b) Prof. Dimitri Basov Final exam, March 18 (Version A) Instructions A. There are 20 problems on this exam. Any 16 of them count for 100% of your grade. If you answer more than 16 problems CORRECTLY, then you get 100% plus an extra 2.5% for each correct answer after the first 16. B. Please make sure that your name is HANDWRITTEN and your code number and the version of your exam is both BUBBLED IN and HANDWRITTEN in your scantron. 1. A solenoid of radius 2.5 cm has 400 turns and a length of 20 cm. Find (i) it’s inductance and (ii) the rate at which current must change through it to produce an emf of 75 mV. ( μ = 4 π × 10- 7 T · m / A) (a) (i) 2 mH, (ii) 38 A/s (b) (i) 20 mH, (ii) 3.8 A/s (c) (i) 200 mH, (ii) 0.4 A/s (d) (i) 2 H, (ii) 0.04 A/s (e) (i) 20 H, (ii) 0.004 A/s 2. Consider the circuit in the figure with E = 6 . 00 V, L = 8 . 00 mH, and R = 4 . 00 Ω . (i) What is the inductive time con- stant of the circuit? (ii) How long does it take the current to reach 80.0% of its maximum value? (a) (i) 2 ms, (ii) 0.45 ms (b) (i) 2 ms, (ii) 3.22 ms (c) (i) 500 s, (ii) 805 ms (d) (i) 500 s, (ii) 255 ms (e) (i) 500 s, (ii) 112 ms 1 of 7 3. A 24-V battery is connected in series with a resistor and an inductor, where R = 8 . Ω and L = 4 . 0 H. Find the energy stored in the inductor (i) when the current reaches its maximum value and (ii) one time constant after the switch is closed. (a) (i) 18 J, (ii) 2.4 J (b) (i) 18 J, (ii) 7.2 J (c) (i) 18 J, (ii) 30.9 J (d) (i) 18 J, (ii) 48.9 J (e) (i) 18 J, (ii) 133.0 J 4. Two parallel conductors carry currents in opposite directions as shown in the figure. One conductor carries a current of 10.0 A. Point A is the midpoint between the wires, and point C is 5.00 cm to the right of the 10.0-A current. I is adjusted so that the magnetic field at C is zero. Find the value of the current I ....
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This note was uploaded on 03/21/2009 for the course PHYS PHYS 1B taught by Professor Berman during the Winter '09 term at UCSD.

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Final_1Bb_w_solutions - Department of Physics UCSD Winter...

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