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. 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?
Carotid pulse - which is located in the neck next to the Adam's apple.
75 turns.
Disconnect the frame-grounding conductor.
Zero amps.

2. Current in an AC circuit may be measured by...
Grounded phase and ground fault devices were not operating.
Clamp-on ammeter.
3 -979 Volts.
Two speeds

3. What type motor is a wound-rotor induction motor?
The motor rotation is reversed.
15 feet off the ground.
A.C.
277 volts.

4. A transformer with a 1:1 ratio is usually a (an)...
25 feet.
100 turns.
Isolation transformer.
Cut around clothing that has adhered to the burned area.

5. If 2000 watts is read in the primary of a single-phase transformer - What is the wattage in the secondary? (Assuming no losses.)
5:1
Short-circuited after power has been removed.
2000 watts
Shunted and taped

6. The property of an electric circuit that opposes any change in current is called...
Lower current and higher voltage
15 feet off the ground.
7 -630 volts.
Inductance.

7. Alternating current may be defined as...
Current that changes constantly in magnitude and periodically in direction.
Allow for metering voltage and Current.
Lower current and higher voltage
Squirrel-cage rotor.

8. If the conductors of a balanced - three-phase circuit pass through a current transformer - how many amps will flow in the transformer?
Short-circuited after power has been removed.
Zero amps.
Stator windings.
Provides single-phase power to smaller loads such as lights - heaters - etc.

9. At what rate should mouth-to-mouth resuscitation be applied?
Second-degree burn.
An electromagnet.
A step-up transformer.
12 to 15 times a minute.

10. The load to which the secondary winding of a current transformer was connected has opened. The secondary leads should be...
H terminals.
Short-circuited after power has been removed.
200 volts AC.
Draw less current.

11. A burn causing a blister is classified as a...
480 volts.
Short-circuited after power has been removed.
Second-degree burn.
60 Hertz

12. Surface transformer installations - unless constructed to eliminate shock hazards - must be installed at least...
Electro-magnetism for their operation.
Clamp-on ammeter.
12 to 15 times a minute.
15 feet off the ground.

13. The standard frequency of power supplied by the power company is...
600 volts.
60 cycles per second (60 Hertz).
Circuit Breaker.
200 volts AC.

14. Operating coils - motors - transformers - relays and solenoids depend upon...
1 amp.
The current will read zero.
Electro-magnetism for their operation.
Current changing constantly in magnitude and periodically in direction.

15. When not connected to a load - the secondary leads of a current transformer should be...
Current that changes constantly in magnitude and periodically in direction.
X.
Shunted and taped
Hyperventilation.

16. What steps up or steps down AC voltage?
At the source transformer.
Transformer
Hyperventilation.
The chest should rise or inflate.

17. A solenoid coil is...
Capacitance.
277 volts.
Larger than that found in the primary winding.
An electromagnet.

18. The following motor leads are brought out of a 3-phase motor (T1 - T2 - T3 - T4 - T5 - T6). This motor is probably for...
Inductance.
Two speeds
Potential transformer.
The motor rotation is reversed.

19. The standard frequency of alternating current used at a mine is...
60 Hertz
Nearly constant.
60 cycles per second (60 Hertz).
Lower current and higher voltage.

20. Current that changes periodically in direction is...
Alternating current.
A.C.
Zero amps.
At the source transformer.

21. The primary function of a power transformer is to provide...
Full-load - three-phase voltage.
Short-circuited after power has been removed.
7 -630 volts.
Reverse any two-phase leads.

22. The neutral ground-bed electrical power system of an underground mine should be separated from the lightning arrestor grounds by at least...
Allow for metering voltage and Current.
An electrical shock hazard may exist.
25 feet.
X.

23. Not an acceptable method for the installations of surface transformers?
Draw less current.
Electro-magnetism for their operation.
Check to make sure that the victim is not still in contact with the electricity.
They must be installed at least 7 feet above the ground.

24. Compared to the secondary of a loaded - step-down transformer - the primary has...
Lower current and higher voltage.
7 -630 volts.
Cut around clothing that has adhered to the burned area.
Nearly constant.

25. The current on the primary side of a step-down transformer with a 4:1 ratio will be...
Circuit Breaker.
Four times less than that of the secondary.
Two speeds
12 to 15 times a minute.

26. 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?
A step-up transformer.
A.C.
5:1.
200 volts AC.

27. What is a capacitor?
Hyperventilation.
A device used to store electrical energy.
They should be made by the same manufacturer.
25 feet.

28. 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.
75 turns.
A.C.
A step-up transformer.
5:1

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

30. How should clothing be removed from a burn?
Lower current and higher voltage.
Because less current flowing at high voltage causes less line loss per kilowatt.
Transformer
Cut around clothing that has adhered to the burned area.

31. What is the first step to be followed in aiding a victim of electrical shock?
200 volts AC.
Draw less current.
Reverse its rotation.
Check to make sure that the victim is not still in contact with the electricity.

32. 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.
5:1.
Short-circuited after power has been removed.
480 volts.
Reverse its rotation.

33. A control power transformer...
Provides single-phase power to smaller loads such as lights - heaters - etc.
Alternating current.
Check to make sure that the victim is not still in contact with the electricity.
They must be installed at least 7 feet above the ground.

34. Three-phase AC underground cables must be provided with overcurrent protection using a...
The motor rotation is reversed.
Potential transformer.
Electro-magnetism for their operation.
Circuit Breaker.

35. How do you change the direction of a 3-phase AC motor?
800 volts.
Reverse any two-phase leads.
Potential transformer.
At least two phases

36. Where should grounding resistors be located?
Larger than that found in the primary winding.
At the source transformer.
Four times less than that of the secondary.
At least two phases

37. Using a 10:1 ratio transformer - the terminals on the secondary side or lower voltage side would be marked...
Capacitance.
Electro-magnetism for their operation.
800 volts.
X.

38. The primary leads of a single-phase transformer should be connected to the...
Second-degree burn.
H terminals.
600 volts.
A grounding resistor.

39. The main function of CT's and PT's on a main substation is to...
Shunted and taped
Two speeds
Inductance.
Allow for metering voltage and Current.

40. If a voltmeter were placed between two phase leads of a three-phase 480-volt system - the meter would read...
480 volts.
7 -630 volts.
Full-load - three-phase voltage.
150 turns.

41. Why is 440-volt - three-phase power more commonly used in mining than 220-volt - three-phase power?
Current that changes constantly in magnitude and periodically in direction.
12 to 15 times a minute.
Because 440-volt power draws less current so cables and control circuit wiring can be smaller.
100 turns.

42. 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...
Reverse its rotation.
The chest should rise or inflate.
Tied together
Electro-magnetism for their operation.

43. If a voltmeter is connected between a phase lead and the ground of a three-phase 480-volt system - the meter will read...
Shunted and taped
They should be made by the same manufacturer.
Four times less than that of the secondary.
277 volts.

44. If current were flowing through a grounding resistor in a 440-volt - resistance-grounded system - this would probably be because...
They should be made by the same manufacturer.
Draw less current.
Grounded phase and ground fault devices were not operating.
An electrical shock hazard may exist.

45. A wound-rotor induction motor has all the following EXCEPT...
The capacitors should be discharged.
Squirrel-cage rotor.
75 turns.
Transformer

46. All transformers step voltage up or down by...
Potential transformer.
Inductance.
X.
A step-up transformer.

47. If any two-phase wires are reversed on a three-phase motor - the motor will...
600 volts.
7 -630 volts.
75 turns.
Reverse its rotation.

48. Current transformers - or CT's - are used to...
Reduce high AC current to lower values and provide isolation between high voltage circuits and metering.
Disconnect the frame-grounding conductor.
12 to 15 times a minute.
At the source transformer.

49. 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.
Short-circuited after power has been removed.
A.C.
5:1

50. What is the danger when working around capacitors?
Current changing constantly in magnitude and periodically in direction.
An electrical shock hazard may exist.
The sum of the two capacitors.
Second-degree burn.