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Exam 3 FISI-3172 Oct. 27, 2009 Dr. LU (Write your answers on the answer sheets.) 1. When two parallel wires have current flowing in the same direction, the mutual force they experience will be? (5 points) a) attractive. b) repulsive. c) zero. 2. A static electric field is conservative, but an electric field produced by a changing magnetic field is nonconservative. (5 points) a) True. b) False. 3. A time constant of an LR circuit is equal to: (5 points) b) L/R. c) R/L. d) 1/(LR). a) LR. 4. The SI unit for inductance is the. (5 points) a) Newton. b) Faraday. c) Henry. d) Coulomb. 5. A rectangular loop of wire is placed next to a straight wire, as shown in the right Figure. There is a current of 3.5 A in both wires. Determine the magnitude and direction of the net force on the loop. (20 points) 6. A 40.0-cm-long solenoid 1.35 cm in diameter is to produce a field of 0.385 mT at its center. How much current should the solenoid carry if it has 765 turns of wire? (20 points) 7. To make the rod move to the right at speed v, you need to apply an external force on the rod to the right. (a) Determine the magnitude of the required force. (b) What external power is needed to move the rod? (20 points) 8. A 1200-pF capacitor is fully charged by a 500-V dc power supply. It is disconnected from the power supply and is connected, at t = 0, to a 75-mH inductor. Determine: (a) the initial charge on the capacitor; (b) the maximum current; (c) the frequency f and period T of oscillation; and (d) the total energy oscillating in the system. (20 points) Bonus problem (20 points) Determine the direction of the induced current in each loop. Answer sheet Dr. Lu FISI-3172 Name j ().. 5. 1. Section : 10 Z S b c. 4 ;;, ::: J . y-A , \. L...----- _ _ _ I Answer sheet Dr. Lu FISI-3172 Section:._ __ Name._ _ _ _ _ _ _ _ _ ID_ _ _ __ (CA) ~d ) 0 ~b V'\o ;1'\J.",c.~ ) (,lA.. y' . lo 0 0 te (' ~ II\! t" leI ~ _ ---_..... .. .. _ . - - --" -