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AC Theory

Instructions:

Answer 50 questions in 15 minutes.
If you are not ready to take this test, you can study here.
Match each statement with the correct term.
Don't refresh. All questions and answers are randomly picked and ordered every time you load a test.

This is a study tool. The 3 wrong answers for each question are randomly chosen from answers to other questions. So, you might find at times the answers obvious, but you will see it re-enforces your understanding as you take the test each time.

1. Alternating current may be defined as...
The current will read zero.
Current that changes constantly in magnitude and periodically in direction.
7 -630 volts.
75 turns.

2. The property of an electrical circuit that opposes any change in voltage is called...
Capacitance.
At least two phases
Two speeds
Inductance.

3. How can you tell if a victim receiving mouth-to-mouth resuscitation is getting air into the lungs?
Check to make sure that the victim is not still in contact with the electricity.
The chest should rise or inflate.
7 -630 volts.
A device used to store electrical energy.

4. When not connected to a load - the secondary leads of a current transformer should be...
Shunted and taped
Inductance.
They must be installed at least 7 feet above the ground.
Draw less current.

5. What should the duty rating of a grounding resistor be?
Grounded phase and ground fault devices were not operating.
Continuous.
Derive a neutral for grounding purposes.
60 cycles per second (60 Hertz).

6. A transformer with 10 turns on the primary coil and 100 turns on the secondary is classified as...
Because 440-volt power draws less current so cables and control circuit wiring can be smaller.
A step-up transformer.
The capacitors should be discharged.
X.

7. Operating coils - motors - transformers - relays and solenoids depend upon...
3 -979 Volts.
Electro-magnetism for their operation.
The current will read zero.
600 volts.

8. Not a symptom of electrical shock?.
277 volts.
Hyperventilation.
The current will read zero.
Draw less current.

9. What steps up or steps down AC voltage?
Isolation transformer.
At the source transformer.
Provides single-phase power to smaller loads such as lights - heaters - etc.
Transformer

10. What position of a selector switch using a voltmeter would you select to check a 120-volt AC circuit to obtain the most accurate reading?
Derive a neutral for grounding purposes.
200 volts AC.
Electro-magnetism for their operation.
600 volts.

11. A burn causing a blister is classified as a...
Second-degree burn.
277 volts.
They should be made by the same manufacturer.
Inductance.

12. The size of a transformer is measured in...
Lower current and higher voltage.
The chest should rise or inflate.
Kilovolt ampere (KVA).
The current will read zero.

13. The property of an electric circuit that opposes any change in current is called...
277 volts.
Zero amps.
Squirrel-cage induction motor.
Inductance.

14. If you use a clamp-on ammeter or tong tester around all three-phase wires of an energized three- phase circuit simultaneously...
Kilovolt ampere (KVA).
The capacitors should be discharged.
The current will read zero.
Electro-magnetism for their operation.

15. AC voltage is raised or lowered by means of...
Transformers.
The motor rotation is reversed.
5:1
X.

16. The speed of an alternating current - squirrel-cage induction motor is...
Nearly constant.
Larger than that found in the primary winding.
Squirrel-cage rotor.
200 volts AC.

17. Find the turns ratio of a single-phase transformer with the following values: Primary power of 10 KW - secondary current of 200 amps - and primary voltage of 250 volts.
A step-up transformer.
5:1.
Draw less current.
Inductance.

18. Define alternating current...
An electromagnet.
Current changing constantly in magnitude and periodically in direction.
600 volts.
X.

19. The following motor leads are brought out of a 3-phase motor (T1 - T2 - T3 - T4 - T5 - T6). This motor is probably for...
Two speeds
150 turns.
Lower current and higher voltage.
800 volts.

20. What happens to a motor that is connected to a three-phase cable when two of the cable's leads are reversed?
Draw less current.
The motor rotation is reversed.
1 amp.
Alternating current.

21. What value of voltage will be measured from phase-to-phase - in a wye-connected secondary - if 2 -300 volts is measured from phase-to-ground?
The motor rotation is reversed.
60 Hertz
3 -979 Volts.
100 turns.

22. The secondary windings on a 10:1 step-down transformer will have a wire size...
Larger than that found in the primary winding.
Shunted and taped
An electromagnet.
60 Hertz

23. Why is 440-volt - three-phase power more commonly used in mining than 220-volt - three-phase power?
Grounded phase and ground fault devices were not operating.
5:1
Because 440-volt power draws less current so cables and control circuit wiring can be smaller.
H terminals.

24. If current were flowing through a grounding resistor in a 440-volt - resistance-grounded system - this would probably be because...
Draw less current.
Grounded phase and ground fault devices were not operating.
Lower current and higher voltage
60 Hertz

25. How do you change the direction of a 3-phase AC motor?
Reverse any two-phase leads.
Because less current flowing at high voltage causes less line loss per kilowatt.
100 turns.
Disconnect the frame-grounding conductor.

26. The minimum allowable size for trailing cables for mobile haulage equipment powered by alternating current is...
H terminals.
Nearly constant.
No.6 AWG.
277 volts.

27. If a voltmeter is connected between a phase lead and the ground of a three-phase 480-volt system - the meter will read...
At least two phases
Stator windings.
X.
277 volts.

28. The primary leads of a single-phase transformer should be connected to the...
Tied together
100 volts.
H terminals.
A step-up transformer.

29. A transformer with a 1:1 ratio is usually a (an)...
Allow for metering voltage and Current.
Full-load - three-phase voltage.
Draw less current.
Isolation transformer.

30. What is the danger when working around capacitors?
5:1.
75 turns.
An electrical shock hazard may exist.
Check to make sure that the victim is not still in contact with the electricity.

31. Current transformers - or CT's - are used to...
No.6 AWG.
A step-up transformer.
Reduce high AC current to lower values and provide isolation between high voltage circuits and metering.
H terminals.

32. What type motor is a wound-rotor induction motor?
Cut around clothing that has adhered to the burned area.
A.C.
Draw less current.
5:1

33. If the conductors of a balanced - three-phase circuit pass through a current transformer - how many amps will flow in the transformer?
At the source transformer.
Transformer
Lower current and higher voltage.
Zero amps.

34. Which of the following does a squirrel cage induction motor have?
15 feet off the ground.
Circuit Breaker.
Stator windings.
1 amp.

35. The transformer used only to measure voltage is a...
H terminals.
Transformer
Kilovolt ampere (KVA).
Potential transformer.

36. A transformer with 1 -500 turns in the primary winding has a primary voltage of 2 -400 volts and a secondary voltage of 120 volts. How many turns are in the secondary winding?
Inductance.
1 amp.
Capacitance.
75 turns.

37. Under fault conditions - the grounding resistor in a high voltage circuit limits the voltage drop in the grounding circuit external to the resistor to not more than...
Shunted and taped
A.C.
X.
100 volts.

38. Two 10-hp induction motors are operating on 460 volts AC. One motor is connected by single- phase; the other is connected in three-phase. The three-phase will...
Alternating current.
Hyperventilation.
Draw less current.
277 volts.

39. The combined capacitance of two capacitors in parallel is...
The sum of the two capacitors.
Two speeds
A device used to store electrical energy.
15 feet off the ground.

40. A transformer has a primary voltage of 2 -400 volts and a secondary reading of 120 volts. If there are 1 -500 turns on the primary - how many turns are on the secondary?
Second-degree burn.
Transformers.
Carotid pulse - which is located in the neck next to the Adam's apple.
75 turns.

41. Compared to the secondary of a loaded - step-down transformer - the primary has...
Potential transformer.
Lower current and higher voltage.
Reverse any two-phase leads.
Derive a neutral for grounding purposes.

42. A transformer has 1 -600 turns in the primary and 400 turns in the secondary. The primary voltage is 2 -400 volts. What is the secondary voltage?
100 volts.
A step-up transformer.
600 volts.
The motor rotation is reversed.

43. If any two-phase wires are reversed on a three-phase motor - the motor will...
Squirrel-cage induction motor.
H terminals.
A device used to store electrical energy.
Reverse its rotation.

44. Compared to the secondary of a loaded - step-down transformer - the primary has...
Lower current and higher voltage
A device used to store electrical energy.
Because 440-volt power draws less current so cables and control circuit wiring can be smaller.
A step-up transformer.

45. At what rate should mouth-to-mouth resuscitation be applied?
12 to 15 times a minute.
5:1
It provides good speed control.
60 cycles per second (60 Hertz).

46. Which of the following is not needed when using an ohmmeter to determine if a motor is grounded?
5:1
Lower current and higher voltage.
Capacitance.
Disconnect the frame-grounding conductor.

47. What is a capacitor?
A step-up transformer.
Carotid pulse - which is located in the neck next to the Adam's apple.
They should be made by the same manufacturer.
A device used to store electrical energy.

48. Three-phase AC underground cables must be provided with overcurrent protection using a...
150 turns.
Isolation transformer.
Circuit Breaker.
25 feet.

49. The load to which the secondary winding of a current transformer was connected has opened. The secondary leads should be...
Short-circuited after power has been removed.
Inductance.
A device used to store electrical energy.
Squirrel-cage induction motor.

50. If a voltmeter were placed between two phase leads of a three-phase 480-volt system - the meter would read...
480 volts.
Kilovolt ampere (KVA).
Squirrel-cage rotor.
Squirrel-cage induction motor.