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Chapter 21 Alternating Current
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1. What is the period for a frequency of 60 Hz?
A. 60 s
B. (1/60) s
C. 120 s
D. (1/120) s
E. (1/377) s
3. The average value of sin2ωt for a complete cycle is:
A. 1.
B. 0.
C. 0.707.
D. 0.500.
E. 0.250.
4. A 150 W light bulb is designed for an ac voltage of 120 V rms. What is the resistance of the bulb?
A. 150 Ω
B. 144 Ω
C. 96.0 Ω
D. 68.0 Ω
E. 48.0 Ω
5. A 150 W light bulb is operating on a 120 V rms ac line. What is the rms current in the bulb?
A. 2.50 A
B. 1.67 A
C. 1.50 A
D. 1.25 A
E. 0.883 A
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6. What is the peak (maximum) power dissipated by a 150 W light bulb attached to a 120 V rms ac line?
A. 300 W
B. 212 W
C. 150 W
D. 106 W
E. 75.0 W
9. What is the capacitive reactance of an 8.00 μF V capacitor attached to 120 V rms at 60.0 Hz?
A. 166 Ω
B. 332 Ω
C. 663 Ω
D. 480 Ω
E. 960 Ω
11. What is the average power for an 8.00 mF capacitor attached to a 120 V rms 60.0 Hz source?
A. 240 W
B. 120 W
C. 85.0 W
D. 60.0 W
E. 0.000
12. What is the inductive reactance of a 200 mH inductor attached to a 120 V rms 60.0 Hz source?
A. 12.0 Ω
B. 75.4 Ω
C. 188 Ω
D. 940 Ω
E. 24.0 Ω
13. What is the rms current in a 200 mH inductor attached to a 120 V rms 60.0 Hz source?
A. 600 A
B. 12.0 A
C. 1.59 A
D. 100 A
E. 1.00 A
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15. What is the inductance for an inductor with a reactance of 20 Ω at a frequency of 60 Hz?
A. 12 H
B. 19 H
C. 3.0 H
D. 53 mH
E. 27 mH
19. An ac circuit has a resistance of 120 Ω and an impedance of 200 Ω. What is the power factor for this
circuit?
A. 0.53
B. 0.32
C. 0.60
D. 1.7
E. 1.3
22. A series LR circuit dissipates 60 W. The circuit is powered by a 120 V rms 60 Hz supply. If the current is
2.0 A rms, what is the power factor?
A. 0
B. 0.25
C. 0.50
D. 0.75
E. 1.0
32. In an ac circuit, the current in an inductor:
A. leads the voltage by 90°.
B. lags the voltage by 90°.
C. is in phase with the voltage.
D. leads the voltage by π radians.
E. lags the voltage by π radians.
37. The voltage supplied to an ac circuit is given by v = 120 sin(60t). What are the rms voltage and the
frequency?
A. 120 V, 60 Hz
B. 120 V, 380 Hz
C. 170 V, 9.5 Hz
D. 85 V, 9.5 Hz
E. 240 V, 30 Hz
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38. A 1500 W hair dryer is run on a 120 V rms circuit. If the circuit breaker is chosen from breakers with the
ratings below, which is the lowest-rated current breaker of the following that won't open the circuit?
A. 10 A
B. 15 A
C. 20 A
D. 30 A
E. 60 A
39. A 2.2 kΩ resistor and a 2.0 μF capacitor are in series in an ac circuit. The rms voltages across each are
equal. What is the frequency?
A. 23 Hz
B. 15 Hz
C. 72 Hz
D. 36 Hz
E. Insufficient information to solve
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