(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
- 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