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. Which of the following is not needed when using an ohmmeter to determine if a motor is grounded?
Disconnect the frame-grounding conductor.
Draw less current.
No.6 AWG.
H terminals.

2. The combined capacitance of two capacitors in parallel is...
A step-up transformer.
The sum of the two capacitors.
Stator windings.
An electromagnet.

3. 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.
Check to make sure that the victim is not still in contact with the electricity.
Larger than that found in the primary winding.
480 volts.

4. Compared to the secondary of a loaded - step-down transformer - the primary has...
Reverse any two-phase leads.
3 -979 Volts.
Lower current and higher voltage
Four times less than that of the secondary.

5. Why is 440-volt - three-phase power more commonly used in mining than 220-volt - three-phase power?
The sum of the two capacitors.
Disconnect the frame-grounding conductor.
Because 440-volt power draws less current so cables and control circuit wiring can be smaller.
Inductance.

6. 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.
Current that changes constantly in magnitude and periodically in direction.
Nearly constant.
Transformer

7. The following motor leads are brought out of a 3-phase motor (T1 - T2 - T3 - T4 - T5 - T6). This motor is probably for...
At the source transformer.
Two speeds
Draw less current.
The capacitors should be discharged.

8. When connecting 3 single-phase transformers into a three-phase system - which of the following is NOT required for the single-phase transformers.
They should be made by the same manufacturer.
An electromagnet.
7 -630 volts.
Inductance.

9. A transformer with a 1:1 ratio is usually a (an)...
Four times less than that of the secondary.
At the source transformer.
Isolation transformer.
150 turns.

10. 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.
2000 watts
Derive a neutral for grounding purposes.
60 cycles per second (60 Hertz).
5:1

11. When troubleshooting a circuit with a bank of capacitors - what precautions must be taken?
Provides single-phase power to smaller loads such as lights - heaters - etc.
Larger than that found in the primary winding.
Stator windings.
The capacitors should be discharged.

12. Not an acceptable method for the installations of surface transformers?
Isolation transformer.
They must be installed at least 7 feet above the ground.
Check to make sure that the victim is not still in contact with the electricity.
Zero amps.

13. 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...
Tied together
A grounding resistor.
100 volts.
Cut around clothing that has adhered to the burned area.

14. How should clothing be removed from a burn?
A device used to store electrical energy.
Tied together
Cut around clothing that has adhered to the burned area.
Provides single-phase power to smaller loads such as lights - heaters - etc.

15. 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?
1 amp.
75 turns.
Four times less than that of the secondary.
Derive a neutral for grounding purposes.

16. What should the duty rating of a grounding resistor be?
Continuous.
Hyperventilation.
Reverse any two-phase leads.
Four times less than that of the secondary.

17. AC voltage is raised or lowered by means of...
Transformers.
Inductance.
3 -979 Volts.
Cut around clothing that has adhered to the burned area.

18. How do you change the direction of a 3-phase AC motor?
Tied together
Shunted and taped
They should be made by the same manufacturer.
Reverse any two-phase leads.

19. If any two-phase wires are reversed on a three-phase motor - the motor will...
It provides good speed control.
Carotid pulse - which is located in the neck next to the Adam's apple.
Reverse its rotation.
X.

20. A current transformer has a ratio of 350:5. If the phase current is 70 amperes - what would be the secondary current?
Because 440-volt power draws less current so cables and control circuit wiring can be smaller.
Larger than that found in the primary winding.
It provides good speed control.
1 amp.

21. Alternating current may be defined as...
The current will read zero.
Current that changes constantly in magnitude and periodically in direction.
75 turns.
277 volts.

22. 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

23. 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?
200 volts AC.
75 turns.
Four times less than that of the secondary.
A grounding resistor.

24. 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.
Stator windings.
The current will read zero.
Tied together

25. A transformer with 10 turns on the primary coil and 100 turns on the secondary is classified as...
800 volts.
No.6 AWG.
A step-up transformer.
Shunted and taped

26. The secondary windings on a 10:1 step-down transformer will have a wire size...
Larger than that found in the primary winding.
2000 watts
The motor rotation is reversed.
Because 440-volt power draws less current so cables and control circuit wiring can be smaller.

27. Three-phase AC underground cables must be provided with overcurrent protection using a...
Stator windings.
A.C.
5:1
Circuit Breaker.

28. What type motor is a wound-rotor induction motor?
7 -630 volts.
H terminals.
It provides good speed control.
A.C.

29. The property of an electrical circuit that opposes any change in voltage is called...
Capacitance.
At the source transformer.
Tied together
Draw less current.

30. If 13 -200 volts are measured from phase-to-phase across a wye-connected secondary - What is the phase-to-ground voltage?
Reverse any two-phase leads.
The motor rotation is reversed.
1 amp.
7 -630 volts.

31. Where should grounding resistors be located?
Derive a neutral for grounding purposes.
75 turns.
At the source transformer.
Provides single-phase power to smaller loads such as lights - heaters - etc.

32. If a voltmeter were placed between two phase leads of a three-phase 480-volt system - the meter would read...
Draw less current.
Transformer
Reduce high AC current to lower values and provide isolation between high voltage circuits and metering.
480 volts.

33. The primary function of a power transformer is to provide...
75 turns.
Second-degree burn.
Full-load - three-phase voltage.
Transformers.

34. A control power transformer...
Because 440-volt power draws less current so cables and control circuit wiring can be smaller.
Electro-magnetism for their operation.
Derive a neutral for grounding purposes.
Provides single-phase power to smaller loads such as lights - heaters - etc.

35. 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?
Squirrel-cage induction motor.
100 turns.
Four times less than that of the secondary.
Allow for metering voltage and Current.

36. A solenoid coil is...
Transformers.
They should be made by the same manufacturer.
An electromagnet.
Zero amps.

37. The speed of an alternating current - squirrel-cage induction motor is...
277 volts.
No.6 AWG.
The current will read zero.
Nearly constant.

38. 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.
Shunted and taped
An electrical shock hazard may exist.
The current will read zero.

39. The minimum allowable size for trailing cables for mobile haulage equipment powered by alternating current is...
The sum of the two capacitors.
Stator windings.
No.6 AWG.
The motor rotation is reversed.

40. When not connected to a load - the secondary leads of a current transformer should be...
Shunted and taped
X.
It provides good speed control.
Lower current and higher voltage.

41. To protect against over-current in a three-phase circuit over-current protection must be provided for...
Reverse any two-phase leads.
Stator windings.
At least two phases
It provides good speed control.

42. What happens to a motor that is connected to a three-phase cable when two of the cable's leads are reversed?
The motor rotation is reversed.
Shunted and taped
Derive a neutral for grounding purposes.
Squirrel-cage induction motor.

43. At what rate should mouth-to-mouth resuscitation be applied?
12 to 15 times a minute.
Isolation transformer.
5:1.
Stator windings.

44. Current transformers - or CT's - are used to...
Second-degree burn.
Isolation transformer.
Reduce high AC current to lower values and provide isolation between high voltage circuits and metering.
Larger than that found in the primary winding.

45. How can you tell if a victim receiving mouth-to-mouth resuscitation is getting air into the lungs?
Potential transformer.
A grounding resistor.
5:1
The chest should rise or inflate.

46. The load to which the secondary winding of a current transformer was connected has opened. The secondary leads should be...
Reverse its rotation.
Current that changes constantly in magnitude and periodically in direction.
Short-circuited after power has been removed.
150 turns.

47. The purpose of a zig-zag transformer is to...
60 cycles per second (60 Hertz).
Derive a neutral for grounding purposes.
5:1
At least two phases

48. Current in an AC circuit may be measured by...
Squirrel-cage induction motor.
800 volts.
Current that changes constantly in magnitude and periodically in direction.
Clamp-on ammeter.

49. Operating coils - motors - transformers - relays and solenoids depend upon...
Transformers.
3 -979 Volts.
Electro-magnetism for their operation.
The capacitors should be discharged.

50. What steps up or steps down AC voltage?
Shunted and taped
Alternating current.
60 cycles per second (60 Hertz).
Transformer