Chapter 31 Electromagnetic Oscillations and Alternating Current In

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)

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) 30 N, west (4) 30 N, east (5) none of these I N 50 B

Suppose this page is perpendicular to a uniform magnetic field and the magnetic flux through it is 5 Wb. If the page is turned by 30◦ around an edge the flux through it will be: A. 2. 5 Wb B. 4. 3 Wb C. 5 Wb D. 5. 8 Wb E. 10 Wb

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. 7 m, is: A. 0 B. 1. 8 m. V C. 3. 6 m. V D. 6. 4 m. V E. 13 m. V

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

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Transmission lines Erms =735 k. V , I rms = 500 A Step-down Step-up transformer T 1 Power Station (31 - 24) home transformer 110 V R = 220Ω T 2

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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. 10 V

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