(Last Updated On: December 8, 2017)

This is the Textbook Assignment: Chapter 1, “Concepts of Alternating Current” from the Module 2 — Introduction to Alternating Current and Transformers in **Navy Electricity and Electronics Training Series (NEETS) **. If you are looking for a reviewer in Electronics Engineering this will definitely help. I can assure you that this will be a great help in reviewing the book in preparation for your Board Exam. Make sure to familiarize each and every questions to increase the chance of passing the ECE Board Exam.

### Start Practice Exam Test Questions

**Choose the letter of the best answer in each questions.**

1. Alternating current can be defined as current that varies in

- A. amplitude and direction
- B. magnitude and phase
- C. amplitude and time
- D. time and phase

2. Before a 120-volt dc source can be used to power a 12-volt load, the voltage must be reduced. Which of the following methods can be used?

- A. A resistor placed in parallel with the load
- B. A resistor placed in series with the load
- C. A step-down transformer placed in series with load
- D. A step-down transformer placed in parallel-with the load

3. Alternating current has replaced direct current in modern transmission systems because it has which of the following advantages?

- A. Ac can be transmitted with no line loss
- B. Ac can be transmitted at higher current levels
- C. Ac can be transmitted at lower voltage levels
- D. Ac can be readily stepped up or down

4. A waveform is a graphic plot of what quantities?

- A. Current versus time
- B. Amplitude versus time
- C. Voltage versus amplitude
- D. Magnitude versus amplitude

5. Which of the following properties surrounds a current-carrying conductor?

- A. A magnetic field
- B. A repulsive force
- C. An attractive force
- D. An electrostatic field

9. Which of the following statements accurately describes the magnetic field surrounding a current-carrying conductor?

- A. It is parallel to and equal along all parts of the conductor
- B. It is parallel to and maximum at the most negative part of the conductor
- C. It is perpendicular to and equal along all parts of the conductor
- D. It is perpendicular to the conductor and maximum at the most negative point of the conductor

10. Which of the following factors determine(s) the intensity of a magnetic field surrounding a coil?

- A. The amount of current flow through the coil
- B. The type of core material
- C. The number of turns in the conductor
- D. All of these

11. When you grasp a coil in your left hand with your thumb pointing in the direction of the north pole, your fingers will be wrapped around the coil in the direction of the

- A. voltage potential
- B. magnetic field
- C. current flow
- D. south pole

12. The power consumed in a conductor in realigning the atoms which set up the magnetic field is known as what type of loss?

- A. Hysteresis loss
- B. Magnetic loss
- C. Field loss
- D. Heat loss

13. The magnetic field surrounding a straight conductor is (a) what shape, and (b) is in what position relative to the conductor?

- A. (a) Linked oblong (b) Parallel
- B. (a) Concentric circles (b) Parallel
- C. (a) Linked oblong (b) Perpendicular
- D. (a) Concentric circles (b) Perpendicular

14. Why is a two-pole magnetic field set up around a coil?

- A. Because separate lines of magnetic force link and combine their effects
- B. Because concentric lines of force cross at right angles and combine.
- C. Because lines of force are separated and bent at the coil ends
- D. Because separate lines of force are attracted to the two poles of the coil

15. When a conductor is moving parallel to magnetic lines of force, (a) what relative number of magnetic lines are cut, and (b) what relative value of emf is induced?

- A. (a) Minimum, (b) maximum
- B. (a) Minimum, (b) minimum
- C. (a) Maximum, (b) maximum
- D. (a) Maximum, (b) minimum

16. When the induced voltage in a conductor rotating in a magnetic field is plotted against the degrees of rotation, the plot will take what shape?

- A. A circle
- B. A sine curve
- C. A square wave
- D. A straight line

17. When a loop of wire is rotated through 360º in a magnetic field, the induced voltage will be zero at which of the following points?

- A. 45º
- B. 90º
- C. 180º
- D. 270º

18. When a loop of wire is rotated 360º in a magnetic field, at what points will the induced voltage reach its maximum (a) positive, and (b) negative values?

- A. (a) 0º , (b) 180º
- B. (a) 0º , (b) 270º
- C. (a) 90º , (b) 180º
- D. (a) 90º , (b) 270º

19. When a coil of wire makes eight complete revolutions through a single magnetic field, (a) what total number of alternations of voltage will be generated

and, (b) what total number of cycles of ac will be generated?

- A. (a) 32, (b) 16
- B. (a) 16, (b) 8
- C. (a) 8, (b) 4
- D. (a) 4, (b) 2

20. According to the left-hand rule for generators, when your thumb points in the direction of rotation, your (a) forefinger and (b) your middle finger will indicate the relative directions of what quantities?

- A. (a) Current, (b) Magnetic flux, south to north
- B. (a) Current, (b) Magnetic flux, north to south
- C. (a) Magnetic flux, south to north, (b) Current
- D. (a) Magnetic flux, north to south, (b) Current

21. Continuous rotation of a conductor through magnetic lines of force will produce what type of (a) voltage and (b) waveform?

- A. (a) Ac, (b) sine wave
- B. (a) Dc, (b) continuous level
- C. (a) Ac, (b) sawtooth
- D. (a) Dc, (b) pulsating wave

22. What is the term for the number of complete cycles of ac produced in one second?

- A. Period
- B. Waveform
- C. Frequency
- D. Wavelength

23. What is the unit of measurement for frequency?

- A. Cycle
- B. Hertz
- C. Period
- D. Maxwell

24. A loop of wire rotating at 60 rpm in a magnetic field will produce an ac voltage of what frequency?

- A. 1 Hz
- B. 60 Hz
- C. 120 Hz
- D. 360 Hz

25. An ac voltage of 250 hertz has a period of

- A. 0.004 second
- B. 0.025 second
- C. 0.4 second
- D. 2.5 seconds

26. What is the approximate frequency of an ac voltage that has a period of .0006 second?

- A. 6 Hz
- B. 16.67 Hz
- C. 600 Hz
- D. 1667 Hz

37. An ac voltage has a frequency of 350 Hz. In two seconds, what total number of times will the peak value of voltage be generated?

- A. 350 times
- B. 700 times
- C. 1400 times
- D. 2800 times

38. The value of current of an ac waveform taken at any particular moment of time is what type of value?

- A. Average value
- B. Effective value
- C. Instantaneous value
- D. Peak-to-peak value

39. While the value of an ac voltage may be expressed as one of several values, the accepted practice is to express it as what type value?

- A. Average value
- B. Instantaneous value
- C. Peak-to-peak value
- D. Effective value

40. The total of ten instantaneous values of an alternation divided by ten is equal to what value?

- A. The peak value
- B. The average value
- C. The instantaneous value
- D. The effective value

41. Which of the following mathematical formulas is used to find the average value of voltage for an ac voltage?

- A. Eavg = 0.707 x Emax
- B. Eavg = 1.414 x Eeff
- C. Eavg = 0.636 x Emax
- D. Eavg = 0.226 x Eeff

42. What is the average value of all of the instantaneous voltages occurring during one cycle of an ac waveform with a peak value of 60 volts?

- A. 0 volts
- B. 38 volts
- C. 76 volts
- D. 128 volts

43. If an ac voltage has an Emax of 220 volts, what is Eavg?

- A. 50 volts
- B. 140 volts
- C. 156 volts
- D. 311 volts

44. If an ac waveform has a peak-to-peak value of 28 volts, what is Eavg?

- A. 40 volts
- B. 20 volts
- C. 18 volts
- D. 9 volts

45. If an ac waveform has a peak value of 4.5 amperes, what is its average value?

- A. 2.9 amperes
- B. 3.2 amperes
- C. 5.7 amperes
- D. 6.4 amperes

46. If the average value of current of an ac waveform is 1.2 amperes, what is its maximum value of current?

- A. 0.8 amperes
- B. 0.9 amperes
- C. 1.7 amperes
- D. 1.9 amperes

47. The value of alternating current that will heat a resistor to the same temperature as an equal value of direct current is known as

- A. Iavg
- B. Ieff
- C. I
~~in~~ - D. Imax

48. The rms value for an ac voltage is equal to what other ac value?

- A. Eavg
- B. Emax
- C. Eeff
- D. Ein

49. What value will result by squaring all values for Einst, averaging these values, and then taking the square root of that average?

- A. Eavg
- B. Emax
- C. Eeff
- D. Ein

50. The accepted, nominal value for household power in the United States is 120-volts, 60 Hz. What is the value of maximum voltage?

- A. 170 volts
- B. 120 volts
- C. 85 volts
- D. 76 volts

51. An ac voltmeter is usually calibrated to read which of the following ac values?

- A. Average
- B. Effective
- C. Peak
- D. Peak-to-peak

52. If the maximum value for an ac voltage is known, the Eeff can be found by using which of the following formulas?

- A. Eeff = Emax/0.636
- B. Eeff = Emax/0.707
- C. Eeff = Emax x 0.707
- D. Eeff = Emax x 1.414

53. If the Ieff of an ac waveform is 3.25 amperes, what is Imax?

- A. 4.6 amperes
- B. 2.3 amperes
- C. 2.1 amperes
- D. 1.6 amperes

54. If the rms value of the voltage of an ac waveform is 12.4 volt what is its average value? (Hint: compute Emaxfirst.)

- A. 8 volts
- B. 11 volts
- C. 15 volts
- D. 18 volts

61. Which of the following is an important rule to remember when using Ohm’s Law to solve ac circuit problems?

- A. Always solve for resistance first
- B. Give the answer as effective value
- C. Never mix values
- D. Convert all given values to effective before attempting to solve

62. An ac circuit is composed of three 20 – ohm resistors connected in parallel. The average voltage supplied to this circuit is 62-volts ac. What is the maximum current?

- A. 9.3 amperes
- B. 14.6 amperes
- C. 17.5 amperes
- D. 22.5 amperes

63. If the ac source in question 1-62 is raised to an average value of 120 volts, what is the Ieff?

- A. 11.48 amperes
- B. 12.70 amperes
- C. 20.01 amperes
- D. 25.52 amperes

64. If Eeff is 150 volts and Imax is 4.5 amperes, what is the total resistance (RT) of a circuit?

- A. 21.2
- B. 23.6
- C. 33.3
- D. 47.1

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