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General > Basic Electricity > Flashcards

Basic Electricity Flashcards

0
Q

What is the basic unit of inductance?

A

The henry.

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1
Q

What is meant by inductance?

A

The ability to store electrical energy in electromagnetic fields.

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3
Q

What does inductive and capacitive reactance cause?

A

Opposition to current flow in AC circuits.

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4
Q

What constitutes a capacitor?

A

Two conductors separated by an insulator.

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5
Q

What is the purpose of a capacitor?

A

It stores electrical energy in electrostatic fields.

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6
Q

What is the basic unit of capacitance?

A

The farad.

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7
Q

Why should electrolytic capacitors not be used in an AC circuit?

A

They are polarized. An electrolytic capacitor will pass current of one polarity, but will block current of the opposite polarity.

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10
Q

Why should Nickel Cadmium and Lead Acid batteries not be stored together?

A

They are chemically opposite and can neutralize each other.

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11
Q

What three things must all electrical circuits contain?

A

A source of electrical energy, a load to use the energy, and conductors to join the source and the load.

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12
Q

What is Ohm’s Law?

A

E = I x R

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13
Q

Name the elements of Ohm’s Law.

A

Voltage, current, and resistance (volts, amps, and ohms).

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14
Q

What is the basic unit of electrical power in a DC circuit?

A

The watt.

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15
Q

What are three types of DC circuits, with regard to the placement of various circuit components?

A

Series, parallel, and series parallel (complex).

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16
Q

What happens in a DC circuit if the voltage is increased but the resistance remains the same?

A

The current increases.

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17
Q

What could be the problem if a Nickel Cadmium battery fails to deliver?

A

A cell imbalance or bad cells.

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18
Q

What are the advantages of Alternating Current?

A

It can be transmitted more readily over long distances, and can be stepped up or down by use of transformers.

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19
Q

What are some things a multi-meter can be used to check?

A

Amps, volts, ohms.

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20
Q

What is meant by impedance?

A

The total opposition to the flow of alternating current. It is the vector sum of resistance, capacitive reactance and inductive reactance.

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21
Q

How many cells are there in a 24-volt lead-acid battery?

A

12 cells (2v each).

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22
Q

What is the specific gravity of the electrolyte in a fully charged lead-acid battery?

A

Between 1.275 - 1.300.

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23
Q

What are the effects temperature has on the specific gravity of the electrolyte in a lead-acid battery?

A

The electrolyte is less dense at higher temperatures and more dense at lower temperatures.

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24
Q

Why is no specific gravity check done on Nickel Cadmium batteries?

A

There is no real change of the specific gravity of the electrolyte during charge or discharge of a Nickel Cadmium battery.

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25
Q

How can you find the polarity of an electromagnet?

A

Hold the electromagnet in your left hand with your fingers encircling the coil in the direction the electrons flow. Your thumb will point to the north end of the electromagnet.

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26
Q

In what units is impedance measured?

A

In ohms.

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27
Q

What is meant by a kilowatt?

A

1,000 watts.

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28
Q

What is the range of temperatures of the electrolyte in a lead-acid battery that does not require that you apply a correction when measuring its specific gravity?

A

Between 70 degrees and 90 degrees Fahrenheit.

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29
Q

What instrument is used to measure the specific gravity of the electrolyte in a lead-acid battery?

A

A hydrometer.

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30
Q

How do you treat a lead-acid battery compartment to protect it from corrosion?

A

Paint it with an asphaltic (tar base) paint or with polyurethane enamel.

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31
Q

What is used to neutralize spilled electrolyte from a lead-acid battery?

A

A solution of bicarbonate of soda and water.

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32
Q

How high should the electrolyte be in a properly serviced lead-acid battery?

A

Only up to the level of the indicator in the cell.

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33
Q

What precautions should be taken in a maintenance shop where both lead-acid and nickel-cadmium batteries are serviced?

A

The two types of batteries should be kept separate, and the tools used on one type should not be used on the other.

34
Q

Why is a hydrometer not used to measure the state of charge of a nickel-cadmium battery?

A

The electrolyte of a nickel-cadmium battery does not enter into the chemical changes that occur when the battery is charged or discharged. Its specific gravity does not change appreciably.

35
Q

What is used to neutralize spilled electrolyte from a nickel-cadmium battery?

A

A solution of boric acid and water.

36
Q

What is meant by electromagnetic induction?

A

The transfer of electrical energy from one conductor to another that is not electrically connected.

37
Q

How many ohms are in a megaohm?

A

One million (1,000,000).

38
Q

What part of an amp is a milliamp?

A

One thousandth (0.001).

39
Q

Does a capacitor in an AC circuit cause the current to lead or lag the voltage?

A

It causes the current to lead the voltage.

40
Q

Does an inductor in an AC circuit cause the current to lead or lag the voltage?

A

It causes the current to lag the voltage.

41
Q

What is an example of an inductor used in a magneto?

A

The coil.

42
Q

What is meant by a megawatt?

A

1,000,000 watts.

43
Q

What is the formula for power in a DC circuit?

A

Power = Voltage times current (P = E x I).

44
Q

What is the relationship between mechanical and electrical power?

A

1 horsepower = 746 watts.

45
Q

What is meant by true power in an AC circuit?

A

Product of the circuit voltage and the current that is in phase with this voltage.

46
Q

In what units is true power expressed?

A

In watts.

47
Q

What is meant by apparent power in an AC circuit?

A

The product of the circuit voltage and the circuit current.

48
Q

In what units is apparent power expressed?

A

In volt-amps.

49
Q

What is meant by reactive power in an AC circuit?

A

The power consumed in the inductive and capacitive reactances in an AC circuit. Reactive power is also called wattless power.

50
Q

In what units is reactive power expressed?

A

In volt-amps reactive (VAR), or kilovolt-amps reactive (KVAR).

51
Q

What is meant by power factor in an AC circuit?

A

The ratio of true power to apparent power. It is also the ratio of circuit resistance to circuit impedance.

52
Q

What is voltage?

A

Electrical pressure.

53
Q

What instrument is used to measure voltage?

A

A voltmeter.

54
Q

To measure voltage, is a voltmeter placed in series or in parallel with the source of voltage?

A

In parallel.

55
Q

What is electrical current?

A

The flow of electrons in a circuit.

56
Q

What instrument is used to measure current flow?

A

An ammeter.

57
Q

What two things happen when current flows through a conductor?

A

Heat is generated and a magnetic field surrounds the conductor.

58
Q

To measure current through a component, is an ammeter placed in parallel or in series with the component?

A

In series.

59
Q

What is meant by continuity in an electrical circuit?

A

The circuit is continuous (or complete) when electrons can flow from one terminal of the power source to the other.

60
Q

What instrument is used to measure continuity in an electrical circuit?

A

An ohmeter.

61
Q

When measuring resistance of a component with an ohmmeter, should the circuit be energized?

A

No, there should be no power on the circuit.

62
Q

What happens to the current in a conductor if the length of the conductor is doubled with all other parameters unchanged?

A

It would decrease to one half.

63
Q

What is meant by the capacity rating of a lead-acid battery?

A

The number of hours a battery can supply a given current flow.

64
Q

In what units is battery capacity expressed?

A

In ampere-hours.

65
Q

What electrolyte is used in a lead-acid battery?

A

A mixture of sulfuric acid and water.

66
Q

Does the specific gravity of the electrolyte in a lead-acid battery increase or decrease as the battery becomes discharged?

A

It decreases.

67
Q

Why is the closed-circuit voltage of a lead-acid battery lower than its open-circuit voltage?

A

Voltage is dropped across the internal resistance of the battery.

68
Q

What is the open-circuit voltage of a lead-acid cell?

A

2.1 volts.

69
Q

What gases are released when a lead-acid battery is being charged?

A

Hydrogen and oxygen.

70
Q

What is the electrolyte used in a nickel-cadmium battery?

A

Potassium hydroxide and water.

71
Q

Is the electrolyte level of a nickel-cadmium battery lowest when the battery is fully charged or fully discharged?

A

Fully discharged.

72
Q

What is a result of cell imbalance in a nickel-cadmium battery?

A

The low internal resistance allows current to flow between the unbalanced cells and generate heat.

73
Q

What is a thermal runaway?

A

The large current flow allowed by the low internal resistance causes the middle cells to produce more heat than they can dissipate. The heat further lowers the internal resistance so more current can flow; this continues until the battery destroys itself.

74
Q

How may thermal runaway be prevented?

A

By carefully monitoring the temperature of the middle cells and controlling the charging current to prevent an excess of current flowing into the battery.

75
Q

How is it possible to know when a nickel-cadmium battery is fully charged?

A

Completely discharge the battery and give it a constant-current charge to 140% of its ampere-hour capacity.

76
Q

What are five sources of electrical energy?

A

Magnetism, chemical energy, light, heat and pressure.

77
Q

What four things affect the resistance of an electrical conductor?

A

The material, the cross-sectional area, the length and the temperature.

78
Q

How can you tell the resistance of a composition resistor?

A

By a series of colored bands around one end of the resistor.

79
Q

What does the specific gravity of the electrolyte of a lead-acid battery indicate?

A

The amount of acid relative to the water in the electrolyte. This is an indication of the state of charge of the battery.

General (12 decks)

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