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. What is the first step to be followed in aiding a victim of electrical shock?
60 Hertz
Check to make sure that the victim is not still in contact with the electricity.
Short-circuited after power has been removed.
Because less current flowing at high voltage causes less line loss per kilowatt.

2. If any two-phase wires are reversed on a three-phase motor - the motor will...
Capacitance.
Stator windings.
Reverse its rotation.
Allow for metering voltage and Current.

3. 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?
75 turns.
Kilovolt ampere (KVA).
200 volts AC.
Current that changes constantly in magnitude and periodically in direction.

4. Operating coils - motors - transformers - relays and solenoids depend upon...
Electro-magnetism for their operation.
800 volts.
Inductance.
Stator windings.

5. A transformer with a 1:1 ratio is usually a (an)...
Provides single-phase power to smaller loads such as lights - heaters - etc.
Zero amps.
Isolation transformer.
150 turns.

6. Where should grounding resistors be located?
At the source transformer.
X.
60 cycles per second (60 Hertz).
Second-degree burn.

7. 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?
Four times less than that of the secondary.
60 cycles per second (60 Hertz).
100 turns.
Check to make sure that the victim is not still in contact with the electricity.

8. The property of an electrical circuit that opposes any change in voltage is called...
1 amp.
Capacitance.
5:1
Draw less current.

9. The main function of CT's and PT's on a main substation is to...
150 turns.
Allow for metering voltage and Current.
They must be installed at least 7 feet above the ground.
Transformer

10. 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?
3 -979 Volts.
Provides single-phase power to smaller loads such as lights - heaters - etc.
The capacitors should be discharged.
Derive a neutral for grounding purposes.

11. The secondary windings on a 10:1 step-down transformer will have a wire size...
Stator windings.
Larger than that found in the primary winding.
480 volts.
Full-load - three-phase voltage.

12. The transformer used only to measure voltage is a...
A grounding resistor.
600 volts.
Potential transformer.
Full-load - three-phase voltage.

13. If the conductors of a balanced - three-phase circuit pass through a current transformer - how many amps will flow in the transformer?
Zero amps.
Clamp-on ammeter.
A.C.
Kilovolt ampere (KVA).

14. If 13 -200 volts are measured from phase-to-phase across a wye-connected secondary - What is the phase-to-ground voltage?
200 volts AC.
At the source transformer.
7 -630 volts.
Transformers.

15. What type motor is a wound-rotor induction motor?
A.C.
The motor rotation is reversed.
100 turns.
1 amp.

16. AC voltage is raised or lowered by means of...
Because 440-volt power draws less current so cables and control circuit wiring can be smaller.
Cut around clothing that has adhered to the burned area.
600 volts.
Transformers.

17. A solenoid coil is...
An electromagnet.
Inductance.
75 turns.
Inductance.

18. High voltage is used to transmit power over long distances...
2000 watts
Because less current flowing at high voltage causes less line loss per kilowatt.
Provides single-phase power to smaller loads such as lights - heaters - etc.
Circuit Breaker.

19. What happens to a motor that is connected to a three-phase cable when two of the cable's leads are reversed?
Kilovolt ampere (KVA).
The motor rotation is reversed.
Cut around clothing that has adhered to the burned area.
2000 watts

20. Current in an AC circuit may be measured by...
Clamp-on ammeter.
7 -630 volts.
75 turns.
Full-load - three-phase voltage.

21. Define alternating current...
Current changing constantly in magnitude and periodically in direction.
Larger than that found in the primary winding.
Reverse any two-phase leads.
Full-load - three-phase voltage.

22. 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...
60 Hertz
Continuous.
It provides good speed control.
Draw less current.

23. How can you tell if a victim receiving mouth-to-mouth resuscitation is getting air into the lungs?
The chest should rise or inflate.
Two speeds
Capacitance.
60 cycles per second (60 Hertz).

24. Alternating current may be defined as...
600 volts.
Current that changes constantly in magnitude and periodically in direction.
The motor rotation is reversed.
60 cycles per second (60 Hertz).

25. Current that changes periodically in direction is...
75 turns.
Two speeds
7 -630 volts.
Alternating current.

26. 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.
Alternating current.
5:1.
Shunted and taped
At least two phases

27. If a voltmeter were placed between two phase leads of a three-phase 480-volt system - the meter would read...
Reverse its rotation.
The motor rotation is reversed.
The capacitors should be discharged.
480 volts.

28. The standard frequency of alternating current used at a mine is...
5:1
Second-degree burn.
60 Hertz
The sum of the two capacitors.

29. The primary function of a power transformer is to provide...
Full-load - three-phase voltage.
Larger than that found in the primary winding.
Shunted and taped
Inductance.

30. The most reliable method to use to determine whether or not the heart has stopped is by checking the...

Warning: Invalid argument supplied for foreach() in /var/www/html/basicversity.com/show_quiz.php on line 183

31. The property of an electric circuit that opposes any change in current is called...
25 feet.
Inductance.
Capacitance.
Provides single-phase power to smaller loads such as lights - heaters - etc.

32. 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?
Draw less current.
H terminals.
Squirrel-cage rotor.
75 turns.

33. A control power transformer...
60 cycles per second (60 Hertz).
Provides single-phase power to smaller loads such as lights - heaters - etc.
75 turns.
Hyperventilation.

34. All transformers step voltage up or down by...
5:1.
Potential transformer.
Inductance.
12 to 15 times a minute.

35. Using a 10:1 ratio transformer - the terminals on the secondary side or lower voltage side would be marked...
Nearly constant.
X.
Capacitance.
150 turns.

36. 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...
A step-up transformer.
25 feet.
Draw less current.
1 amp.

37. To protect against over-current in a three-phase circuit over-current protection must be provided for...
At least two phases
12 to 15 times a minute.
Allow for metering voltage and Current.
Because 440-volt power draws less current so cables and control circuit wiring can be smaller.

38. The combined capacitance of two capacitors in parallel is...
Nearly constant.
The sum of the two capacitors.
The current will read zero.
Short-circuited after power has been removed.

39. Not true about AC power?
H terminals.
The capacitors should be discharged.
It provides good speed control.
800 volts.

40. The current on the primary side of a step-down transformer with a 4:1 ratio will be...
At the source transformer.
Four times less than that of the secondary.
They should be made by the same manufacturer.
Two speeds

41. The primary leads of a single-phase transformer should be connected to the...
An electromagnet.
H terminals.
Check to make sure that the victim is not still in contact with the electricity.
Four times less than that of the secondary.

42. 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.
600 volts.
A grounding resistor.
An electrical shock hazard may exist.

43. The standard frequency of power supplied by the power company is...
Current that changes constantly in magnitude and periodically in direction.
Draw less current.
Transformers.
60 cycles per second (60 Hertz).

44. If a voltmeter is connected between a phase lead and the ground of a three-phase 480-volt system - the meter will read...
Squirrel-cage rotor.
Current that changes constantly in magnitude and periodically in direction.
277 volts.
3 -979 Volts.

45. The purpose of a zig-zag transformer is to...
Squirrel-cage rotor.
Derive a neutral for grounding purposes.
Draw less current.
2000 watts

46. If current were flowing through a grounding resistor in a 440-volt - resistance-grounded system - this would probably be because...
Capacitance.
Electro-magnetism for their operation.
Grounded phase and ground fault devices were not operating.
At the source transformer.

47. Not an acceptable method for the installations of surface transformers?
Current that changes constantly in magnitude and periodically in direction.
150 turns.
They must be installed at least 7 feet above the ground.
The capacitors should be discharged.

48. 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.
Provides single-phase power to smaller loads such as lights - heaters - etc.
800 volts.
A device used to store electrical energy.
5:1

49. 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...
Potential transformer.
800 volts.
Tied together
They must be installed at least 7 feet above the ground.

50. When connecting 3 single-phase transformers into a three-phase system - which of the following is NOT required for the single-phase transformers.
A device used to store electrical energy.
Zero amps.
They should be made by the same manufacturer.
Reverse its rotation.