Test your basic knowledge |

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. How can you tell if a victim receiving mouth-to-mouth resuscitation is getting air into the lungs?
Shunted and taped
Draw less current.
It provides good speed control.
The chest should rise or inflate.

2. To protect against over-current in a three-phase circuit over-current protection must be provided for...
X.
At least two phases
The chest should rise or inflate.
100 volts.

3. If you use a clamp-on ammeter or tong tester around all three-phase wires of an energized three- phase circuit simultaneously...
Reverse its rotation.
The current will read zero.
800 volts.
Electro-magnetism for their operation.

4. High voltage is used to transmit power over long distances...
Because less current flowing at high voltage causes less line loss per kilowatt.
Derive a neutral for grounding purposes.
They must be installed at least 7 feet above the ground.
Circuit Breaker.

5. The standard frequency of power supplied by the power company is...
60 cycles per second (60 Hertz).
An electromagnet.
Because less current flowing at high voltage causes less line loss per kilowatt.
100 volts.

6. 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...
Cut around clothing that has adhered to the burned area.
Draw less current.
75 turns.
Alternating current.

7. The load to which the secondary winding of a current transformer was connected has opened. The secondary leads should be...
100 turns.
A device used to store electrical energy.
Circuit Breaker.
Short-circuited after power has been removed.

8. A transformer has 2000 turns in the primary and 500 turns in the secondary. The primary voltage is 3 -200 volts. What is the secondary voltage?
25 feet.
The capacitors should be discharged.
H terminals.
800 volts.

9. Define alternating current...
Second-degree burn.
Short-circuited after power has been removed.
Current changing constantly in magnitude and periodically in direction.
An electromagnet.

10. The property of an electrical circuit that opposes any change in voltage is called...
The sum of the two capacitors.
Capacitance.
No.6 AWG.
5:1.

11. If the conductors of a balanced - three-phase circuit pass through a current transformer - how many amps will flow in the transformer?
Squirrel-cage rotor.
Zero amps.
Four times less than that of the secondary.
Shunted and taped

12. The primary leads of a single-phase transformer should be connected to the...
Kilovolt ampere (KVA).
H terminals.
Transformers.
No.6 AWG.

13. If any two-phase wires are reversed on a three-phase motor - the motor will...
Full-load - three-phase voltage.
Second-degree burn.
Reverse any two-phase leads.
Reverse its rotation.

14. 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.
1 amp.
Alternating current.
An electrical shock hazard may exist.
5:1.

15. What is the first step to be followed in aiding a victim of electrical shock?
Nearly constant.
Short-circuited after power has been removed.
Lower current and higher voltage
Check to make sure that the victim is not still in contact with the electricity.

16. Not a symptom of electrical shock?.
Shunted and taped
H terminals.
480 volts.
Hyperventilation.

17. 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?
600 volts.
A grounding resistor.
Squirrel-cage induction motor.
Allow for metering voltage and Current.

18. AC voltage is raised or lowered by means of...
Nearly constant.
150 turns.
Carotid pulse - which is located in the neck next to the Adam's apple.
Transformers.

19. The combined capacitance of two capacitors in parallel is...
Current changing constantly in magnitude and periodically in direction.
The chest should rise or inflate.
The sum of the two capacitors.
60 Hertz

20. What type motor is a wound-rotor induction motor?
7 -630 volts.
A grounding resistor.
An electromagnet.
A.C.

21. A transformer has a primary voltage of 2 -800 volts and a secondary reading of 140 volts. If there are 2000 turns on the primary - how many turns are on the secondary?
100 turns.
Grounded phase and ground fault devices were not operating.
Zero amps.
An electrical shock hazard may exist.

22. A current transformer has a ratio of 350:5. If the phase current is 70 amperes - what would be the secondary current?
Isolation transformer.
1 amp.
It provides good speed control.
5:1.

23. Should a ground fault occur - what device can be installed to limit the current in the neutral of a three-phase AC system?
A grounding resistor.
Draw less current.
Inductance.
600 volts.

24. Find the turns ratio of a single-phase transformer with the following values: Primary power of 5KW - secondary current of 100 amps - and primary voltage of 250 volts.
5:1
75 turns.
An electrical shock hazard may exist.
Current that changes constantly in magnitude and periodically in direction.

25. When connecting 3 single-phase transformers into a three-phase system - which of the following is NOT required for the single-phase transformers.
Cut around clothing that has adhered to the burned area.
Squirrel-cage induction motor.
They should be made by the same manufacturer.
H terminals.

26. If 13 -200 volts are measured from phase-to-phase across a wye-connected secondary - What is the phase-to-ground voltage?
12 to 15 times a minute.
Transformer
7 -630 volts.
100 volts.

27. The speed of an alternating current - squirrel-cage induction motor is...
Nearly constant.
A step-up transformer.
H terminals.
Allow for metering voltage and Current.

28. 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?
75 turns.
Squirrel-cage rotor.
An electrical shock hazard may exist.
The chest should rise or inflate.

29. 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...
100 volts.
Short-circuited after power has been removed.
Squirrel-cage rotor.
Larger than that found in the primary winding.

30. At what rate should mouth-to-mouth resuscitation be applied?
Derive a neutral for grounding purposes.
3 -979 Volts.
12 to 15 times a minute.
25 feet.

31. What is a capacitor?
A device used to store electrical energy.
3 -979 Volts.
Squirrel-cage rotor.
Reverse any two-phase leads.

32. Why is 440-volt - three-phase power more commonly used in mining than 220-volt - three-phase power?
Because 440-volt power draws less current so cables and control circuit wiring can be smaller.
Carotid pulse - which is located in the neck next to the Adam's apple.
5:1.
800 volts.

33. A burn causing a blister is classified as a...
Reduce high AC current to lower values and provide isolation between high voltage circuits and metering.
Second-degree burn.
Larger than that found in the primary winding.
60 Hertz

34. 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?
3 -979 Volts.
Isolation transformer.
200 volts AC.
Short-circuited after power has been removed.

35. The transformer used only to measure voltage is a...
75 turns.
Potential transformer.
480 volts.
Derive a neutral for grounding purposes.

36. Alternating current may be defined as...
Grounded phase and ground fault devices were not operating.
2000 watts
Current that changes constantly in magnitude and periodically in direction.
X.

37. The primary function of a power transformer is to provide...
Draw less current.
Full-load - three-phase voltage.
A step-up transformer.
No.6 AWG.

38. What steps up or steps down AC voltage?
Stator windings.
Transformer
Lower current and higher voltage
Inductance.

39. A transformer with a 1:1 ratio is usually a (an)...
They must be installed at least 7 feet above the ground.
25 feet.
Isolation transformer.
277 volts.

40. Which of the following is not needed when using an ohmmeter to determine if a motor is grounded?
Disconnect the frame-grounding conductor.
Full-load - three-phase voltage.
An electrical shock hazard may exist.
Check to make sure that the victim is not still in contact with the electricity.

41. The size of a transformer is measured in...
12 to 15 times a minute.
Tied together
Derive a neutral for grounding purposes.
Kilovolt ampere (KVA).

42. If current were flowing through a grounding resistor in a 440-volt - resistance-grounded system - this would probably be because...
Continuous.
Grounded phase and ground fault devices were not operating.
15 feet off the ground.
A.C.

43. When troubleshooting a circuit with a bank of capacitors - what precautions must be taken?
75 turns.
A grounding resistor.
Lower current and higher voltage.
The capacitors should be discharged.

44. Operating coils - motors - transformers - relays and solenoids depend upon...
200 volts AC.
Electro-magnetism for their operation.
Circuit Breaker.
The sum of the two capacitors.

45. The property of an electric circuit that opposes any change in current is called...
No.6 AWG.
Second-degree burn.
Inductance.
Nearly constant.

46. The minimum allowable size for trailing cables for mobile haulage equipment powered by alternating current is...
Two speeds
Transformers.
No.6 AWG.
X.

47. The standard frequency of alternating current used at a mine is...
200 volts AC.
Zero amps.
12 to 15 times a minute.
60 Hertz

48. What type of 3-phase AC motor is used most often around a mine?
The motor rotation is reversed.
Squirrel-cage induction motor.
Cut around clothing that has adhered to the burned area.
2000 watts

49. Current in an AC circuit may be measured by...
Clamp-on ammeter.
480 volts.
The motor rotation is reversed.
Zero amps.

50. The neutral ground-bed electrical power system of an underground mine should be separated from the lightning arrestor grounds by at least...
Current that changes constantly in magnitude and periodically in direction.
Reverse any two-phase leads.
Shunted and taped
25 feet.