Reference no: EM131081089
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1. Which one of the following statements is true concerning an AC circuit that contains both resistance and inductance?
A. The current and voltage will be in phase.
B. The current will lag the voltage.
C. The current will lead the voltage.
D. The voltage will lag the current.
2. In a certain balanced three-phase system, each line current is 5 A and each line voltage is 220 V. What is the approximate real power, if the power factor is 0.7?
A. 1100 W
B. 1334 W
C. 154 W
D. 1770 W
3. There are many different values associated with an AC sine wave. Which one of the following continually changes throughout the cycle?
A. instantaneous value
B. peak value
C. effective value
D. average value
4. What is the real power (rounded) of a balanced, three-phase, Y-connected system that has a power factor of 0.9, an effective line current of 50 A and a phase voltage of 200 V?
A. 15.5 KW
B. 26.9 KW
C. 90 KW
D. 9 KW
5. A full cycle of AC power consists of two
A. phases
B. alternations
C. pulses
D. Degrees
6. A technician uses an oscilloscope to measure the peak value of an AC wave. He tells you that the voltage has a peak value of 100 V. What is the rms value of the voltage?
A. 100 V
B. 10 V
C. 707 V
D. 70.7 V
7. How long does it take one cycle of 60 Hz current to complete one positive and one negative alternation?
A. 1/120 second
B. 1/180 second
C. 1/60 second
D. 1/360 second
8. The peak value of a sine wave is 80 VAC. What is the peak-to-peak value of this waveform?
A. 60 V
B. 160 V
C. 120 V
D. 40 V
9. The peak value of a sine wave is equal to 240 VAC. What is the average value of the waveform?
A. 169.68 V
B. 152.64 V
C. 120.74 V
D. 144.14 V
10. The average value of a sine wave is 83 VAC. What is the peak value (rounded) of the sine wave?
A. 110.9 V
B. 145.2 V
C. 115.6 V
D. 130.5 V
11. At what voltage level is AC power normally created by the utility?
A. 1000 VAC
B. 2500 VAC
C. 500 VAC
D. 1300 VAC
12. In a modern industrial plant, the most likely polyphase power system in use is a
A. one-phase system.
B. two-phase system.
C. four-phase system.
D. three-phase system.
13. When you're using the right-hand, or generator, rule your middle finger indicates the direction of what?
A. Conventional current flow
B. Magnetic field
C. Coil movement
D. Electron current flow
14. If a motor designed for 50 or 60 cycle operation is connected to 60 Hz current, the motor will
A. turn faster.
B. stall easily.
C. produce less torque.
D. overheat and fail.
15. Another name for the Y- or wye-connected system of polyphase power is the
A. delta system.
B. balanced system.
C. star system.
D. split-phase system.
16. The total number of AC cycles completed in one second is the current's
A. alteration
B. phase
C. timing
D. frequency
17. In order to reduce inductive reactance, what devices are normally placed on transmission or distribution lines?
A. Capacitors
B. Shunt reactors
C. Resistors
D. Semiconductors
18. If the resistance in an AC circuit is 100 OHMS and the impedance is 120 OHMS, what is the circuit's power factor (rounded)?
A. 0.707
B. 0.833
C. 0.714
D. 0.631
19. The peak value of an AC sine wave is 120 V. What is the average value (rounded)?
A. 25.5 V
End of exam
B. 76.3 V
C. 84.8 V
D. 46.8 V
20. An AC sine wave has an RMS value of 100 V. What is the average of the waveform?
A. 80 V
B. 102 V
C. 90 V
D. 92.6 V
21. If the phase angle in a circuit is 45 degrees, what is the power factor of this circuit?
A. 0
B. 0.707
C. 0.45
D. 0.15
22. In a three-phase power system, the phases of each voltage are normally separated by how many time
degrees?
A. 90
B. 120
C. 60
D. 180
23. AC power is created by using
A. Batteries
B. an AC generator
C. Transformers
D. an AC motor
24. If an AC current begins rising positive at 0 degrees, when will it reach its negative maximum current?
A. 180º
B. 270º
C. 90º
D. 360º
25. Which one of the following values exactly matches the rms value of an AC signal?
A. Effective
B. Average
C. Peak-to-peak
D. Peak
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