1. Chapter 31 Electromagnetic Oscillations and Alternating Current In this chapter we will cover the following topics: -Electromagnetic oscillations in an LC circuit -Alternating current (AC) circuits with capacitors -Resonance in RCL circuits -Power in AC-circuits -Transformers, AC power transmission (31 - 1)

2. A horizontal power line carries a current of 5000 A from south to north. Earth's magnetic eld (60 μT) is directed towards north and inclined down-ward 50 degrees to the horizontal. Find the magnitude and direction of the magnetic force on 100 m of the line due to the Earth's field. (1)23 N, west(2) 23 N, east(3) 30N, west (4) 30N, east (5) none of these 50 B N I

3. Suppose this page is perpendicular to a uniform magnetic field and the magnetic flux through it is 5Wb. If the page is turned by 30◦ around an edge the flux through it will be: A. 2.5Wb B. 4.3Wb C. 5Wb D. 5.8Wb E. 10Wb

4. A car travels northward at 75 km/h along a straight road in a region where Earth’s magnetic field has a vertical component of 0.50 × 10 −4 T. The emf induced between the left and right side, separated by 1.7m, is: A. 0 B. 1.8mV C. 3.6mV D. 6.4mV E. 13mV

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20. Circuit element Average Power ReactancePhase of currentVoltage amplitude Resistor R Current is in phase with the voltage Capacitor C Current leads voltage by a quarter of a period Inductor L Current lags behind voltage by a quarter of a period SUMMARY (31 - 17)

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27. Power Station Transmission lines E rms =735 kV, I rms = 500 A home 110 V T1T1 T2T2 Step-up transformer Step-down transformer R = 220Ω (31 - 24)

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31. Hitt A generator supplies 100 V to the primary coil of a transformer. The primary has 50 turns and the secondary has 500 turns. The secondary voltage is: A. 1000 V B. 500 V C. 250 V D. 100 V E. 10V

32. hitt The main reason that alternating current replaced direct current for general use is: A. ac generators do not need slip rings B. ac voltages may be conveniently transformed C. electric clocks do not work on dc D. a given ac current does not heat a power line as much as the same dc current E. ac minimizes magnetic effects