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. The property of an electrical circuit that opposes any change in voltage is called...
The current will read zero.
Capacitance.
Alternating current.
Because 440-volt power draws less current so cables and control circuit wiring can be smaller.

2. AC voltage is raised or lowered by means of...
Reduce high AC current to lower values and provide isolation between high voltage circuits and metering.
Transformers.
Reverse its rotation.
The capacitors should be discharged.

3. The transformer used only to measure voltage is a...
They must be installed at least 7 feet above the ground.
Stator windings.
Potential transformer.
800 volts.

4. Not a symptom of electrical shock?.
Hyperventilation.
It provides good speed control.
An electrical shock hazard may exist.
Because less current flowing at high voltage causes less line loss per kilowatt.

5. If the conductors of a balanced - three-phase circuit pass through a current transformer - how many amps will flow in the transformer?
150 turns.
Electro-magnetism for their operation.
Hyperventilation.
Zero amps.

6. Not an acceptable method for the installations of surface transformers?
5:1
Reverse its rotation.
They must be installed at least 7 feet above the ground.
Full-load - three-phase voltage.

7. Current that changes periodically in direction is...
Current that changes constantly in magnitude and periodically in direction.
Squirrel-cage induction motor.
Alternating current.
Circuit Breaker.

8. When connecting 3 single-phase transformers into a three-phase system - which of the following is NOT required for the single-phase transformers.
The sum of the two capacitors.
They should be made by the same manufacturer.
Transformers.
100 turns.

9. The standard frequency of power supplied by the power company is...
Derive a neutral for grounding purposes.
60 cycles per second (60 Hertz).
Current changing constantly in magnitude and periodically in direction.
Hyperventilation.

10. At what rate should mouth-to-mouth resuscitation be applied?
Kilovolt ampere (KVA).
12 to 15 times a minute.
480 volts.
The motor rotation is reversed.

11. What type of 3-phase AC motor is used most often around a mine?
A device used to store electrical energy.
Because less current flowing at high voltage causes less line loss per kilowatt.
The sum of the two capacitors.
Squirrel-cage induction motor.

12. High voltage is used to transmit power over long distances...
Draw less current.
Cut around clothing that has adhered to the burned area.
Nearly constant.
Because less current flowing at high voltage causes less line loss per kilowatt.

13. If a voltmeter were placed between two phase leads of a three-phase 480-volt system - the meter would read...
480 volts.
Carotid pulse - which is located in the neck next to the Adam's apple.
Potential transformer.
Second-degree burn.

14. 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?
Reverse its rotation.
3 -979 Volts.
Disconnect the frame-grounding conductor.
5:1.

15. Alternating current may be defined as...
Current that changes constantly in magnitude and periodically in direction.
Second-degree burn.
600 volts.
Alternating current.

16. If a voltmeter is connected between a phase lead and the ground of a three-phase 480-volt system - the meter will read...
The sum of the two capacitors.
Transformer
The current will read zero.
277 volts.

17. How can you tell if a victim receiving mouth-to-mouth resuscitation is getting air into the lungs?
15 feet off the ground.
The chest should rise or inflate.
A grounding resistor.
Inductance.

18. The minimum allowable size for trailing cables for mobile haulage equipment powered by alternating current is...
Hyperventilation.
It provides good speed control.
No.6 AWG.
5:1

19. If 2000 watts is read in the primary of a single-phase transformer - What is the wattage in the secondary? (Assuming no losses.)
2000 watts
Clamp-on ammeter.
Transformers.
5:1.

20. 460 volts AC is required to operate two motors - one connected in single-phase and the other connected in three-phase. The three-phase motor will...
Draw less current.
At the source transformer.
Second-degree burn.
Circuit Breaker.

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?
Derive a neutral for grounding purposes.
100 turns.
At least two phases
Squirrel-cage induction motor.

22. If any two-phase wires are reversed on a three-phase motor - the motor will...
Reverse its rotation.
An electrical shock hazard may exist.
A step-up transformer.
150 turns.

23. If 13 -200 volts are measured from phase-to-phase across a wye-connected secondary - What is the phase-to-ground voltage?
7 -630 volts.
No.6 AWG.
At the source transformer.
Shunted and taped

24. If current were flowing through a grounding resistor in a 440-volt - resistance-grounded system - this would probably be because...
Allow for metering voltage and Current.
800 volts.
Nearly constant.
Grounded phase and ground fault devices were not operating.

25. Not true about AC power?
Transformer
It provides good speed control.
Capacitance.
Second-degree burn.

26. The neutral ground-bed electrical power system of an underground mine should be separated from the lightning arrestor grounds by at least...
25 feet.
480 volts.
Continuous.
2000 watts

27. What should the duty rating of a grounding resistor be?
Continuous.
Capacitance.
Draw less current.
Check to make sure that the victim is not still in contact with the electricity.

28. 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?
800 volts.
Larger than that found in the primary winding.
2000 watts
7 -630 volts.

29. The primary function of a power transformer is to provide...
Full-load - three-phase voltage.
The motor rotation is reversed.
Inductance.
Electro-magnetism for their operation.

30. What happens to a motor that is connected to a three-phase cable when two of the cable's leads are reversed?
It provides good speed control.
The current will read zero.
Inductance.
The motor rotation is reversed.

31. If you use a clamp-on ammeter or tong tester around all three-phase wires of an energized three- phase circuit simultaneously...
600 volts.
The current will read zero.
No.6 AWG.
A.C.

32. A transformer with 10 turns on the primary coil and 100 turns on the secondary is classified as...
2000 watts
A step-up transformer.
Provides single-phase power to smaller loads such as lights - heaters - etc.
Squirrel-cage rotor.

33. A transformer with a 1:1 ratio is usually a (an)...
Hyperventilation.
Isolation transformer.
600 volts.
Reverse its rotation.

34. The combined capacitance of two capacitors in parallel is...
The sum of the two capacitors.
Inductance.
Current that changes constantly in magnitude and periodically in direction.
Clamp-on ammeter.

35. 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...
60 cycles per second (60 Hertz).
150 turns.
At least two phases
Draw less current.

36. Current transformers - or CT's - are used to...
Second-degree burn.
Reduce high AC current to lower values and provide isolation between high voltage circuits and metering.
1 amp.
A.C.

37. 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?
75 turns.
60 cycles per second (60 Hertz).
Potential transformer.
Clamp-on ammeter.

38. The property of an electric circuit that opposes any change in current is called...
Allow for metering voltage and Current.
Inductance.
Check to make sure that the victim is not still in contact with the electricity.
Two speeds

39. What is the first step to be followed in aiding a victim of electrical shock?
No.6 AWG.
Check to make sure that the victim is not still in contact with the electricity.
Stator windings.
277 volts.

40. Where should grounding resistors be located?
At the source transformer.
12 to 15 times a minute.
Derive a neutral for grounding purposes.
Reverse any two-phase leads.

41. Operating coils - motors - transformers - relays and solenoids depend upon...
Electro-magnetism for their operation.
5:1
Derive a neutral for grounding purposes.
At the source transformer.

42. How should clothing be removed from a burn?
Larger than that found in the primary winding.
25 feet.
Cut around clothing that has adhered to the burned area.
Check to make sure that the victim is not still in contact with the electricity.

43. 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?
Alternating current.
75 turns.
Circuit Breaker.
Reduce high AC current to lower values and provide isolation between high voltage circuits and metering.

44. The speed of an alternating current - squirrel-cage induction motor is...
Nearly constant.
Clamp-on ammeter.
H terminals.
The chest should rise or inflate.

45. Current in an AC circuit may be measured by...
Clamp-on ammeter.
Second-degree burn.
7 -630 volts.
Kilovolt ampere (KVA).

46. Should a ground fault occur - what device can be installed to limit the current in the neutral of a three-phase AC system?
25 feet.
Draw less current.
Stator windings.
A grounding resistor.

47. 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?
Inductance.
100 turns.
600 volts.
100 volts.

48. A 3-phase - 2 speed - constant torque motor is running at fast speed. The motor windings are connected wye for fast speed. Motor leads T4 - T5 and T6 are connected to the line leads. Motor leads T1 - T2 and T3 should be...
Tied together
Grounded phase and ground fault devices were not operating.
277 volts.
Full-load - three-phase voltage.

49. A burn causing a blister is classified as a...
Two speeds
Second-degree burn.
The capacitors should be discharged.
5:1.

50. The current on the primary side of a step-down transformer with a 4:1 ratio will be...
Reverse its rotation.
Four times less than that of the secondary.
Kilovolt ampere (KVA).
Derive a neutral for grounding purposes.