ELECTRICAL TRAINING FINAL EXAM

1. Conventional Current Flow is current flow from positive to negative potentials

2. Conventional Current Flow is current flow from positive to negative potentials

3. A shunt-wound DC motor has a decreasing torque as speed increases.

4. A series-wound motor has a rapidly increasing torque when speed decreases.

5. Electron current, or amperage, is described as the movement of free electrons through a conductor.

6. Resistance is defined as all opposition to current flow.

7. In 1827, George Simon Ohm discovered that there was a definite relationship between voltage, current, and resistance in an electrical circuit.

8. The speed of a DC motor may be changed by using resistors to vary the field current and, therefore, the field strength.

9. As load is removed from a shunt-wound motor, the speed will increase sharply.

10. The advantages of a series-wound motor are that it develops a large torque and can be operated at low speed.

11. Starting resistors are necessary for large DC motors to prevent damage due to high currents while starting the motor.

12. Magnetism is a result of ___________ spinning on their own axis around the nucleus.

13. In magnetic materials, the atoms have certain areas called domains.

14. Domains are aligned such that their electrons tend to spin in opposite directions.

15. The law of magnetism states that like magnetic poles repel and unlike magnetic poles attract.

16. The group of magnetic field lines emitted outward from the north pole of a magnet is called magnetic flux.

17. Air, which is nonmagnetic, has a very high BH profile.

18. The permeability (μ) of a magnetic material is the ratio of B to H.

19. The magnetic flux in an iron core lags behind the magnetizing force.

20. The hysteresis loop is a series of curves that show the characteristics of a magnetic material.

21. The maximum number of electrons that can fit in the outermost shell of any atom is 18.

22. The electrons in the outermost shell are called valence electrons.

23. A battery consists of two or more chemical cells connected in series.

24. The chemical cell is composed of two electrodes made of different types of metal or metallic compounds which are immersed in an electrolyte solution.

25. A line diagram is used to show the relationship between component groups, or stages in a circuit.

26. The total voltage across a DC series circuit is equal to the sum of the voltages across each resistor in the circuit.

27. The voltage flowing through each branch of a DC parallel circuit is equal to the total voltage in the circuit.

28. The proton carries a single unit positive charge equal in magnitude to the electron charge.

29. The electrons attraction to the nucleus is called  __________ .

30. The Electrostatic Field is a force acting between charged objects that causes Them to repel or attract.

31. To produce current, the electrons must be moved by a potential difference.

32. Atoms with only one valence electron make good ____________ .

33. All voltages and currents have polarity as well as magnitude.

34. The direction of electron flow is from a point of negative potential to a point of positive potential.

35. The direction of positive charges, or holes, is in the opposite direction of electron flow. This flow of positive charges is known as “conventional flow.”

36. Kirchhoff’s voltage law states that the sum of the voltage drops around a closed loop is equal to the sum of the voltage sources of that loop.

37. Kirchhoff’s current law states that the current arriving at any junction point in a circuit is equal to the current leaving that junction.

38. The voltage flow at any element in a DC circuit can be determined using loop equations.

39. The voltage at any point in a DC circuit can be determined using node equations.

40. An open series DC circuit will result in no power being consumed by any of the loads.

41. An will oppose a change in current flow by the CEMF induced when the field collapses or expands.

42. A capacitor is constructed of two conductors (plates) separated by a dielectric.

43. An electrolyte is a solution which is capable of conducting an electric current. The electrolyte of a cell may be a liquid or a paste.

44. Specific gravity is defined as the ratio comparing the weight of any liquid to the weight of an equal volume of water.

45. A good example of a voltaic cell is one that contains iron and copper electrodes.

46. The purpose of a battery is to store chemical energy and to convert this chemical energy into electrical energy when the need arises.

47. A battery that is connected in parallel has the advantage of a greater                        .

48. As load is removed from a shunt-wound motor, the speed will increase sharply.

49. To reduce the amount of gassing, charging voltages above                       volts per cell should be minimized.

50. Counter-electromotive force (CEMF) is defined as the induced voltage that acts to counter the applied voltage in a DC motor or a DC generator.

51. Applied voltage is defined as the current that is delivered across the load.

52. The                           of an over-compounded DC generator gradually rises with an increasing load.

53. In a differentially-compounded DC generator, the series and shunt fields oppose one another.

54. The speed of a DC motor may be changed by using resistors to vary the field current and, therefore, the field strength.

55. A series-wound motor has a rapidly increasing torque when speed decreases.

56. The advantages of a series-wound motor are that it develops a large torque and can be operated at low speed.

57. Starting resistors are necessary for large DC motors to prevent damage due to high currents while starting the motor.

58. A simple generator consists of a conductor loop turning in a magnetic field, cutting across the magnetic lines of force.

59. The sine wave output is the result of one side of the generator loop cutting lines of force.

60. Effective value of AC equals effective value of DC.

61. A shunt-wound DC motor has a decreasing torque as speed increases.

62. Phase angle is used to compare two wave forms.

63. As the generator coil rotates 180°, the output voltage goes through one complete cycle.

64. The alkaline cell has the advantage of an extended life over that of a carbon-zinc cell of the same size.

65. The nickel-cadmium battery has the advantage of being a dry cell that is a true storage battery with a reversible chemical reaction.

66. Which device below operates on the principals of inductance?

67. Opposition to the flow of alternating current caused by inductance is called capacitive reactance.

68. Current leads voltage by 90 degrees in a purely capacitive circuit.

69. Impedance is the total opposition to current flow in an AC circuit.

70. Impedance is equal to total resistance.

71. R-C-L series circuit at resonance is when net reactance is zero and circuit current output is determined by the series resistance of the circuit.

72. R-C-L parallel circuit at resonance is when net reactance is maximum and circuit current output is at minimum.

73. In AC circuits, current and voltage are normally in phase and, as a result, not all the power produced by the generator can be used to accomplish work.

74. While direct current has one form of power, alternating current has three different forms of power that are related in a unique relationship.

75. True power is the power delivered to an electrical circuit.

76. Apparent power is the power consumed by the resistive loads in an electrical circuit.

77. Reactive power is the power consumed in an AC circuit because of the expansion and collapse of magnetic and electrostatic fields.

78. Reactive power is not useful power because it is stored in the circuit itself.

79. The total power delivered by the source is the apparent power.

80. Power factor is the ratio between true power and apparent power.

81. In a three phase system each phase is                   out of phase with each other.

82. Unbalanced three-phase circuits are indicated by abnormally high currents in one or more of the phases.

83. Slip rings are electrical connections that are used to transfer power to and from the rotor of an AC generator.

84. Efficiency of an AC generator can be calculated by dividing the output by the input and multiplying by 100.

85. The frequency of the generated voltage in an AC generator can be calculated by multiplying the number of                          by the speed of the generator and dividing by a factor of 120.

86. The advantage of the delta-connected AC generator is that if one phase becomes damaged or open, the remaining two phases can still deliver three-phase power at a reduced capacity of 57.7%.

87. The advantage of a wye-connected AC generator is that each phase only has to carry 57.7% of line voltage and, therefore, can be used for high voltage generation.

88. The purpose of a voltage regulator is to maintain the output current of a generator at a desired value.

89. It is virtually impossible for the rotor of an AC induction motor to turn at the same speed as the rotating magnetic field.

90. Slip is the percentage difference between the speed of the rotor and the speed of the rotating magnetic field.

91. Synchronous motors are used to accommodate large loads and to improve the power factor of transformers in large industrial complexes.

92. Transformers are constructed so that their characteristics match the application for which they are intended

93. Electronics or power transformers are sometimes considered to be those with ratings of                    volt-amperes and below.

94. Effective voltage is equal to                        times the peak voltage.

95. Some commonly used methods of cooling distribution transformers are using oil or some other heat-conducting material.

96. The auto transformer is generally used in low power applications where a variable current is required.

97. Average voltage is equal to                         times the peak voltage.

98. Current lags voltage in a purely inductive circuit by a 90° phase angle.

99. Copper loss is power lost in the primary and secondary windings of a transformer due to the ohmic resistance of the windings.

100. The voltage of a shunt-wound DC generator increase with an increase in load current.