Test your basic knowledge |

AC Theory

Subjects : science, engineering
Instructions:
  • Answer 50 questions in 30 minutes. 2 minutes extra for reading the instructions.
  • 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. High voltage is used to transmit power over long distances...






2. Compared to the secondary of a loaded - step-down transformer - the primary has...






3. All transformers step voltage up or down by...






4. Compared to the secondary of a loaded - step-down transformer - the primary has...






5. The current on the primary side of a step-down transformer with a 4:1 ratio will be...






6. Where should grounding resistors be located?






7. Operating coils - motors - transformers - relays and solenoids depend upon...






8. If a voltmeter is connected between a phase lead and the ground of a three-phase 480-volt system - the meter will read...






9. How should clothing be removed from a burn?






10. When connecting 3 single-phase transformers into a three-phase system - which of the following is NOT required for the single-phase transformers.






11. 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?






12. AC voltage is raised or lowered by means of...






13. A burn causing a blister is classified as a...






14. What type of 3-phase AC motor is used most often around a mine?






15. If a voltmeter were placed between two phase leads of a three-phase 480-volt system - the meter would read...






16. Surface transformer installations - unless constructed to eliminate shock hazards - must be installed at least...






17. Should a ground fault occur - what device can be installed to limit the current in the neutral of a three-phase AC system?






18. What is the danger when working around capacitors?






19. 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...






20. 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.






21. If 2000 watts is read in the primary of a single-phase transformer - What is the wattage in the secondary? (Assuming no losses.)






22. Using a 10:1 ratio transformer - the terminals on the secondary side or lower voltage side would be marked...






23. A wound-rotor induction motor has all the following EXCEPT...






24. The following motor leads are brought out of a 3-phase motor (T1 - T2 - T3 - T4 - T5 - T6). This motor is probably for...






25. If current were flowing through a grounding resistor in a 440-volt - resistance-grounded system - this would probably be because...






26. The property of an electric circuit that opposes any change in current is called...






27. The speed of an alternating current - squirrel-cage induction motor is...






28. Which of the following is not needed when using an ohmmeter to determine if a motor is grounded?






29. The standard frequency of alternating current used at a mine is...






30. The size of a transformer is measured in...






31. Not an acceptable method for the installations of surface transformers?






32. A transformer with 3000 turns in the primary winding has a primary voltage of 4 -800 volts and a secondary voltage of 240 volts. How many turns are in the secondary winding?






33. The purpose of a zig-zag transformer is to...






34. What type motor is a wound-rotor induction motor?






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...






36. The neutral ground-bed electrical power system of an underground mine should be separated from the lightning arrestor grounds by at least...






37. The combined capacitance of two capacitors in parallel is...






38. A solenoid coil is...






39. 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?






40. How do you change the direction of a 3-phase AC motor?






41. What is a capacitor?






42. Alternating current may be defined as...






43. The primary leads of a single-phase transformer should be connected to the...






44. What steps up or steps down AC voltage?






45. 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...






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


47. What should the duty rating of a grounding resistor be?






48. If you use a clamp-on ammeter or tong tester around all three-phase wires of an energized three- phase circuit simultaneously...






49. 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?






50. When troubleshooting a circuit with a bank of capacitors - what precautions must be taken?