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General A&P Oral > Fundamentals of Electricity and Electronics > Flashcards

Fundamentals of Electricity and Electronics Flashcards

1
Q

What is the difference between the conventional current flow theory and electron flow?

A

Conventional current flow theory is a visualization of current as flowing from positive to negative. In actual practice, electrons in a circuit flow from negative to positive (electron theory).

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2
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 electrons flow (from negative to positive). Your thumb will point to the north pole of the electromagnet.

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3
Q

What constitutes a capacitor?

A

Two conductors separated by an insulator.

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4
Q

What is the purpose of a capacitor?

A

It stores electrical energy in electrostatic fields.

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5
Q

What is the basic unit of capacitance?

A

The farad.

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6
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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7
Q

What is meant by inductance?

A

The ability to store electrical energy in electromagnetic fields.

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8
Q

What is the basic unit of inductance?

A

The henry.

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9
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.

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10
Q

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

A

It causes the current to lag behind the voltage.

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11
Q

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

A

The watt.

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12
Q

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

A

It increases.

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13
Q

What are five sources of electrical energy?

A

Magnetism, chemical energy, light, heat, and pressure.

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14
Q

Which law of electricity is the most important for an aircraft mechanic to know?

A

Ohm’s law

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15
Q

What are the elements of Ohm’s law?

A

Voltage, Current, and resistance.

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16
Q

What is the name of the law that describes the relationship in an electrical circuit of voltage, current, and resistance?

A

Ohm’s law.

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17
Q

What is the basic equation of Ohm’s law?

A

E=IR

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18
Q

What is Kirchoff’s voltage law?

A

Kirchoff’s voltage law states that the algebraic sum of all voltages around a closed path or loop is zero. Another way of saying it is that the sum of all the voltage drops equal the total source voltage.

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19
Q

What is the formula for determining power?

A

General power formula: P=IE

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20
Q

What is Faraday’s law?

A

Faraday’s law, or the law of electromagnetic induction, states that the induced EMF or electromagnetic force in a closed loop of wire is proportional to the rate of change of the magnetic flux through a coil of wire.

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21
Q

What is Lenz’s law?

A

Lenz’s law states that the EMF induced in a electric circuit always acts in such a direction that the current it drives around a closed circuit produces a magnetic field, which opposes the change in the magnetic flux.

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22
Q

What is the right-hand motor rule?

A

When the index finger of the right hand is pointed in the direction of the magnetic field and the second finger in the direction of current flow, the thumb indicates the direction of the current carrying wire moves.

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23
Q

What is meant by a kilowatt?

A

1000 watts.

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24
Q

What is meant by a magawatt?

A

1,000,000 watts.

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25
Q

What instrument is used to measure current flow?

A

An ammeter.

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26
Q

What is a megaohm?

A

One million ohms.

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27
Q

What instrument is sued to measure electrical resistance?

A

An ohmmeter.

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28
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.

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29
Q

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

A

An ohmmeter.

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30
Q

In what units is battery capacity expressed?

A

In ampere-hours.

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31
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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32
Q

What is voltage?

A

Electrical pressure.

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33
Q

What instrument is ued to measure voltage?

A

A voltmeter.

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34
Q

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

A

In parallel.

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35
Q

What is the voltage across each resistor connected in parallel across a 12-volt battery?

A

12 volts.

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36
Q

What is the basic unit of voltage?

A

The volt.

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37
Q

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

A

2.1 volts.

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38
Q

How is output voltage regulated in an AC alternator?

A

Voltage regulation is accomplished by varying the strength of the AC exciter fields (field voltage).

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39
Q

What is electrical current?

A

The flow of electrons in a circuit.

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40
Q

What is the basic unit of current flow?

A

The ampere.

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41
Q

What part of an amp is a milliamp?

A

One thousandth (0.001) of an amp.

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42
Q

What two things happen when current flows through a conductor?

A

Heat is generated and a magnetic field surrounds the conductor.

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43
Q

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

A

In series.

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44
Q

What formula is used to find current when voltage and resistance are known?

A

I=E/R

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45
Q

What is meant by resistance in an electrical circuit?

A

The opposition to the flow of electrons.

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46
Q

What is the basic unit of electrical resistance?

A

The ohm.

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47
Q

What four things affect the resistance of an electrical conductor.

A

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

48
Q

How can you tell the resistance of a composition resistor?

A

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

49
Q

What formula is used to find resistance when voltage and current are known?

A

R=E/I

50
Q

What is meant by impedance?

A

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

51
Q

In what units is impedance measured?

A

In ohms.

52
Q

How is resistance calculated in a series circuit?

A

For resistors in a series configuration, the total resistance of the circuit is equal to the sum of the individual resistors.

53
Q

What is the total resistance of three 12-ohm resistors connected in series?

A

36 ohms.

54
Q

What is the total resistance of three 12- ohm resistors connected in parallel?

A

4 ohms.

55
Q

What is the formula of power for power in a DC circuit?

A

P=EI

56
Q

What is the relationship between mechanical and electrical power?

A

1 horsepower=746 watts.

57
Q

What is meant by true power in an AC circuit?

A

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

58
Q

In what units is true power expressed?

A

In watts.

59
Q

What is meant by apparent power in an AC circuit?

A

The product of of the circuit voltage and the circuit current, without reference to phase angle.

60
Q

In what units is apparent power expressed?

A

In volt-amps.

61
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.

62
Q

In what units is reactive power expressed?

A

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

63
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 the circuit resistance to circuit impedance.

64
Q

How many watts of power are consumed by a 1/5hp, 24-V DC motor that is 75% efficient?

A

199 watts

65
Q

How much current flows through each of three resistors connected in a series if the total current is 3 amps?

A

3 amps

66
Q

How much current flows through each of three equal resistors connected in parallel if the total current is 3 amps?

A

1 amp.

67
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.

68
Q

What electrolyte is used in a lead-acid battery?

A

A mixture of sulfuric acid and water.

69
Q

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

A

It decreases.

70
Q

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

A

Between 1.275 and 1.300

71
Q

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

A

12

72
Q

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

A

Between 70° F and 90° F.

73
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 a polyurethane enamel.

74
Q

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

A

A solution of bicarbonate of soda and water.

75
Q

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

A

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

76
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.

77
Q

What is the electrolyte used in a Ni-Cad battery?

A

Potassium hydroxide and water.

77
Q

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

A

Hydrogen and oxygen.

78
Q

Why is a hydrometer not used to measure the state of charge of a Ni-Cad battery?

A

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

79
Q

What is a result of cell imbalance in a Ni-Cad battery?

A

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

80
Q

Is the electrolyte level of a Ni-Cad battery lowest when the battery is fully charged or fully discharged.

A

Fully discharged.

81
Q

What is a thermal runaway?

A

The large current flow allowed by the low internal resistance causes the 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.

82
Q

How may thermal runaway be prevented?

A

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

83
Q

How is it possible to know when a Ni-Cad battery is fully charged?

A

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

84
Q

What is used to neutralize spilled electrolyte from a Ni-Cad battery?

A

A solution of boric acid and water.

85
Q

What is a transformer, and how does it work?

A

A transformer is a device that changes electrical energy in an AC circuit of a given voltage into electrical energy at a different voltage level. It consists of two coils that are not electrically connected but arranged so that the magnetic field surrounding one coil cuts through the other coil.

86
Q

What three things must an electrical circuit contain?

A

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

87
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.

88
Q

What is the basic function of a switch?

A

Switches control the current flow in most aircraft electrical circuits.

89
Q

What is a relay?

A

A relay is simply an electromechanical switch where a small amount of current can control a large amount of current.

90
Q

What is the function of a current limiter?

A

A current limiter is a type of heavy-duty fuse, commonly with ratings of 30 amps or greater. They are often used to protect a section of an electrical system, such as a single electrical bus.

91
Q

What materials are fixed resistors made of?

A

The most common fixed resistors are made of carbon composition. Other types of fixed resistors include carbon film, metal-oxide, metal film, and metal glaze. Wire-wound resistors are typically used to control large amounts of current and have high power ratings.

92
Q

What are two main types of variable resistors?

A

The two main types of variable resistors are the rheostat and the potentiometer.

93
Q

How can you tell the resistance of a composition resistor?

A

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

94
Q

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

A

The resistance of the conductor would double and current flow would be decreased.

95
Q

Explain the basic concept of digital logic.

A

Transistors are used in digital electronics to construct circuits that act as digital logic gates. The purpose and task of a device is achieved by manipulating electric signals through the logic gates. Thousands, and even millions, of tiny transistors can be placed on a chip to create the digital logic landscape through which a component’s signals are processed.

96
Q

What is RAM?

A

Random access memory that is used for temporary storage in a computer system.

97
Q

What is ROM?

A

Read-only memory is a type of nonvolatile memory in a computer that is not lost when power to the computer is lost.

98
Q

What is NVRAM?

A

Non-volatile random access memory is random access memory that is retained, even when power is lost.

99
Q

What is a logic gate?

A

Logic gates provide a set output signal based on one or more input signals. The input signal is either voltage (referred to as TRUE, logic 1, or Yes), or not voltage (referred to as False, Logic 0, or No). The basic logic gates are AND, OR, and NOT.

100
Q

What is an inverter in logic function?

A

Converts a 1 to a 0, or a 0 to a 1.

101
Q

What is a rectifier?

A

Converts AC voltage to DC voltage

102
Q

What is a flip-flop?

A

An electrical circuit that can store a single binary signal, either a 1 or a 0. The binary state can change based on the input signal.

103
Q

What are binary numbers?

A

The binary number system has only two digits: 0 and 1. It is also know as a base-2 numbering system.

104
Q

What is electrostatic discharge (or ESD)?

A

ESD is the discharge of static electricity than can build up on a component or a person’s body. ESD is a frequent cause of damage to solid-state components and integrated circuits and can be prevented by wearing a grounding wrist strap when handling electrical components.

105
Q

What type of drawing depicts electrical components with respect to each other within a circuit?

A

An electrical schematic.

106
Q

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

A

Series, parallel, and series-parallel.

107
Q

What are the two general types of AC motors used in aircraft systems?

A

Induction motors and synchronous motors.

108
Q

What is the formula used to determine the speed of an AC motor?

A

RPM=(120xfrequency)/Number of poles

109
Q

In what types of applications is a series wound DC motor most often used?

A

Applications that require high torque and low speed, such as a starter motor.

110
Q

What are two principal parts of a DC motor?

A

The field assembly and an armature assembly.

111
Q

When a volt/ohm multimeter is set to measure current, what precautions should be taken?

A

Never place the multimeter leads across a voltage drop, as this can damage the meter.

112
Q

What precautions should be taken in the maintenance shop where both lead-acid and Ni-Cad 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.

113
Q

What precaution should be taken when working on a high voltage strobe light circuit?

A

Disconnect the power from the strobe power supply and let it stand for 5-10 minutes to allow the capacitors to bleed off.

114
Q

What are some precautions that should be taken when working around an aircraft battery installed in an aircraft?

A
  1. When disconnecting a battery, always disconnect the negative terminal first.
  2. When installing a batter, always connect the negative terminal last.
  3. When the battery is installed, care should be taken to never allow tools or equipment to short the positive terminal to ground.

General A&P Oral (28 decks)

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