M053 Review for Units 1 and 2

1. What are other terms for rise and decay of current and voltage in a circuit?

Increase and decrease of current and voltage in a circuit.

2. When does current reach its maximum value in a resistive circuit?

Instantly when the resistive circuit is energized.

3. Which line represents time and which line current in a time graph?

The horizontal line represents time and the vertical line represents current.

4. What are time constants?

Marks on the time line that show time periods.

5. On a time line, where does the second time period begin?

At T 1.

6. What do T 0, T 1, T 2, T 3, etc., refer to?

Time periods or time constants.

7. What is an LR circuit?

A circuit that has both inductance and resistance.

8. How many time periods does it take for current in a LR circuit to reach maximum value?

Five.

9. How many time constants does it take for current in an LR circuit to decay?

Five.

10. What is the abbreviation for time constant?

TC.

11. What is the term used to identify/measure time constants?

Milliseconds or microseconds.

12. What is the Universal Time Constant Chart?

A graph which shows percentage values on the rise and decay curves at each of the five time constants.

13. What is the mathematical formula for time constants?

TC=L/R

14. What is a growth curve?

A curve that shows the rise of current.

15. What is the percentage value on a decay curve at T 3 ?

5%.

16. What is the percentage value on a growth curve at T 4 ?

98%.

17. What is a capacitor?

An electrical device that stores energy and then releases it later.

18. What are the two conducting surfaces of a capacitor called?

Plates.

19. What is another term that is often used instead of the word “capacitor”?

Condenser.

20. What types of non-conducting material can be used to separate the plates of a capacitor?

Air, paper, or liquid.

21. When is a capacitor said to be charged?

When it has potential difference between the two plates.

22. What is capacitance?

The ability of two conducting surfaces, separated by some form of non-conducting material, to store an electrical charge.

23. What factors determine the capacitance of a capacitor?

1. The surface are of the plates., 2. The distance between the plates., and 3. The dielectric used between the plates.

24. What effect does the amount of voltage applied to a capacitor have in the capacitance?

No effect.

25. What happens to capacitance if the plate areas of a capacitor are doubled?

The capacitance is doubled.

26. What are dielectric constants?

The numerical ratings given dielectric materials based on their relationship to air.

27. How do you find total capacitance in a series circuit?

Use the same rule for determining total resistance in a parallel circuit.

28. What is capacitive reactance?

The opposition to current flow that a capacitor offers in an AC circuit.

29. What is the unit of measurement of capacitance?

The farad.

30. How many farads is a picofarad?

1/1,000,000,000,000 of a farad.

31. How is capacitive reactance (X C ) measured?

In ohms.

32. When will current flow stop in a DC circuit with a capacitor wired into it?

When capacitor voltage equals applied voltage.

33. What is another name for a vacuum tube?

An electron tube.

34. What do you call a tube from which all of the air has been removed?

A vacuum tube.

35. Which is the positive electrode in a vacuum tube?

The anode.

36. What is the name of the negative electrode in a vacuum tube?

The cathode.

37. What is the name of the glass or metal housing around a vacuum tube?

An envelope.

38. What electronic elements are found inside a vacuum tube?

Electrodes.

39. What is the giving off of electrons from a heated cathode called?

Emitting electrons.

40. What is another term for cathode.

Emitter.

41. Which electrode is sometimes called the emitter?

The cathode.

42. Which electrode is sometimes called the collector?

The anode.

43. What is the heater wire in a vacuum tube called?

A filament wire.

44. When is the cathode in a vacuum tube said to be directly heated?

When the cathode and the filament are the same.

45. How many electrodes are in a diode?

Two.

46. What is a triode?

A vacuum tube that has three electrodes.

47. What is the wire screen in a vacuum tube called?

A grid.

48. What does the control grid do in a vacuum tube?

It controls the flow of electrons from the cathode to the anode.

49. What are the electrodes in a triode?

The cathode, the anode, and the control grid.

50. What do you call a vacuum tube with four electrodes?

A tetrode.

51. What are the four electrodes in a tetrode?

The anode, the cathode, the screen grid, and the control grid.

52. What is a pentode?

A vacuum tube which contains five electrodes.

53. What are the five electrodes in a pentode?

The cathode, the anode, the control grid, the screen grid, and the suppressor grid.

54. What can a vacuum tube be used for?

To change AC current to DC and to increase the strength of an electrical signal.

55. How does a transistor differ from a vacuum tube?

Transistors weigh less, are smaller but stronger than vacuum tubes, and require no warm-up time.

56. What can very hot weather do to a transistor?

It can cause the transistor to stop working.

57. What are the three basic parts of a transistor?

The emitter, the base, and the collector.

58. What are two types of materials that transistors are made from?

P-type and N-type material.

59. What elements are in P- type material?

Germanium and indium.

60. What part of a transistor is comparable to the cathode in a vacuum tube?

The emitter.

61. Where is the base of a transistor located?

Between the emitter and the collector.

62. What is the collector in a transistor comparable to in a vacuum tube?

An anode.

63. What is a PNP transistor?

One in which the emitter and collector are made of P-type material.

64. Which direction does current flow in an NPN transistor?

From the emitter to the collector.

65. What is the primary use of a transistor?

As a current-, voltage-, or power- amplifying device.

66. What does a rectifier do?

Changes alternating current to pulsating direct current.

67. What is an amplifier?

An electronic component that amplifies a signal.

68. What is gain?

The ratio of output to input signal.

69. What is the simplest type of amplifier?

A single-ended amplifier.

M053 Review for Units 3 and 4

1. What device transfers electrical energy from one circuit to another by electromagnetic induction?

A transformer.

2. What type of transformer transfers a high voltage to a low voltage?

A step-down transformer.

3. What two types of cores are used for transformers?

An iron core and an air core.

4. Does a transformer have an AC or a DC source for continuous output?

An AC source.

5. How does a transformer transfer electrical energy from one circuit to another?

By electromagnetic induction.

6. What are the main shapes used for iron-core transformers?

Hollow core and shell.

7. What is another name for a shell-type core?

E- and I- type core.

8. Which transformer core is the most commonly used?

The shell-type core.

9. Which winding on a transformer is connected to the power source?

The primary winding.

10. What is the secondary winding on a transformer connect to?

The load.

11. What is the simplest type of transformer winding?

The single-secondary transformer.

12. When is a multi-secondary transformer used?

When more than one voltage is required.

13. What type of transformer secondary has two equal outputs of opposite polarity?

A center-tapped transformer.

14. What is a 1:1 ratio transformer?

A transformer in which the source voltage matches the voltage required by the rest of the power supply.

15. What kind of transformer loss occurs as a result of the small amount of resistance present in any coil or wire?

Copper loss.

16. What can be done to reduce copper loss?

Windings are made of low- resistance copper.

17. What do you call the power loss caused by random current flow within a core?

Eddy-current loss.

18. How are transformer cores made in order to reduce eddy- current loss?

They are made with laminated slices of steel insulated with varnish.

19. What is hysteresis loss?

The energy lost when aligning the magnetic units within the core when the field changes direction.

20. How does an increase in frequency of the applied voltage affect hysteresis loss?

A greater loss through heat dissipation occurs when the frequency of applied voltage is increased.

21. What type of transformer core is used to reduce hysteresis loss?

Air cores.

22. What type of transformer core is used with frequencies in the audio range?

Iron cores.

23. What type of transformer loss can be thought of as resulting from a kind of friction?

Hysteresis loss.

24. What happens to current when frequency is increased in a transformer?

Current is decreased.

25. What is determined by the type and thickness of the insulation of the windings of a transformer?

The voltage-handling capacity.

26. What determines the power- handling capacity of a transformer?

The cooling ability of the transformer.

27. What is determined by the diameter of the wire used in the windings of a transformer?

The current-handling capacity.

28. What is indicated on the front or side of a transformer?

The voltage-, current-, and power- handling capacity.

29. What is a diode?

A device that allows current to flow easily in one direction, but offers opposition to current flow in the other direction.

30. What is the function of a rectifier in a circuit?

It converts AC voltage into pulsating DC voltage.

31. When does reverse bias exist?

When the cathode is more positive than the anode.

32. What is an alternation?

Half of a cycle.

33. What is the key to rectifier operation?

A diode.

34. What two alternations does a cycle of AC have?

Positive and negative alternation.

35. What does a half-wave rectifier block?

Either the positive or negative alternation of the AC circuit in the transformer secondary.

36. What is negative pulsating DC voltage?

The voltage produced from the output of a rectifier when the rectifier blocks the positive AC half-cycles.

37. How many diodes does a half wave rectifier have?

One.

38. What is the simplest rectifier circuit?

A half-wave rectifier circuit.

39. What is positive pulsating DC voltage?

The voltage produced from the output of a rectifier when the rectifier blocks the negative AC half-cycle.

40. What does the diode block in a half-wave rectifier?

Either the positive or negative alternation of the AC current in the secondary.

41. Which output voltage has less variation, the output from a full-wave rectifier, or the output from a half wave rectifier?

Full-wave rectifier output voltage.

42. How many diodes are there in a full-wave rectifier?

Two.

43. Which rectifier uses two diodes to convert each negative and positive alternation of the input AC voltage to one polarity at the output?

A full-wave rectifier.

44. What does the center-tapped transformer do in the transformer secondary?

It splits the secondary AC voltage into two equal AC voltages.

45. How many diodes are conducting at a given time in a bridge rectifier?

Two.

46. How many diodes does a bridge rectifier have?

Four.

47. How are the diodes in a bridge rectifier arranged?

In a diamond pattern.

48. What is the main advantage of using a full-wave rectifier?

There is low voltage variation in the output.

49. What is the main advantage of using a bridge rectifier?

It has low voltage variation and high voltage output.

50. What are the disadvantages of a full-wave rectifier?

It has more components than a half-wave rectifier, and it has low output voltage.