E2 > E2 Theory Terms > Flashcards

E2 Theory Terms Flashcards

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1
Q

Magnet

A

material that attracts a number of other materials such as iron, nickel and cobalt.

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2
Q

Permanent magnet

A

a magnet that does not require any power or force to maintain its magnetic field.

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3
Q

Magnetic Flux

A

Magnetic lines of force

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4
Q

Flux density

A

the amount of magnetic flux concentrated in a given area.

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5
Q

Electromagnet

A

a magnet that requires electric current flow to maintain its magnetic field.

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6
Q

Ampere-turns

A

turns of the coil times the current flowing through the coil

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7
Q

Magnetomotive Force (mmf)

A

total force producing a magnetic field.

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8
Q

Reluctance

A

the ability of a material to resist magnetism.

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9
Q

Permeability

A

the ability of a material to become magnetized.

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10
Q

Saturation

A

when all molecules of a magnetic material are aligned.

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11
Q

Retentivity

A

the ability of a material to remain magnetized after the magnetizing force is removed.

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12
Q

Residual Magnetism

A

the amount of magnetism left in a material after the magnetizing force has been removed.

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13
Q

Solenoid

A

a magnetic coil that converts electrical current into linear mechanical motion.

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14
Q

Induced voltage

A

voltage produced through use of magnetic force.

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15
Q

Weber

A

100 million lines of flux

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16
Q

Lenz’s Law

A

“an induced voltage or current opposes the motion that causes it.”

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17
Q

Inductor

A

an electrical device that stores energy in electromagnetic form and opposes a change in current.

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18
Q

Inductance (L)

A

the ability of an inductor to store energy in electromagnetic form.

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19
Q

Henrys (H)

A

Unit of measure of inductance.

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20
Q

Generator

A

a device that converts mechanical energy into electrical energy.

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21
Q

Armature

A

the rotating part of a DC machine that contains the electricity producing coils & commutator.

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22
Q

Neutral plane

A

the armature coil position in which no voltage or torque is being produced.

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23
Q

Armature Reaction

A

distortion of the main magnetic field caused by the magnetic field generated in the armature.

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24
Q

Copper losses

A

power losses due to current flowing through the coils, AKA, I²R losses.

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25
Self-excited
derives excitation current from residual magnetism in the pole pieces.
26
Separately excited
derives excitation current from an exterior source.
27
Armature coil
the rotating part of a DC machine that generates electricity and torque.
28
Brushes
stationary blocks used to convey electricity to or from the armature.
29
Commutator
the part of the armature that acts as a mechanical rectifier or inverter (ensures current is flowing in the correct direction).
30
Field windings
windings in a DC machine used to provide the main magnetic field.
31
Pole pieces
the core material or permanent magnets that provide the main magnetic field.
32
Interpoles
small additional pole pieces used to correct armature reaction.
33
Motor
a device that converts electrical energy into (rotational) mechanical energy.
34
Revolutions per minute (RPM)
measure of rotational speed.
35
Rotor
the rotating part of the machine.
36
Stator
the stationary part of the machine.
37
Torque
measure of rotational force measured in lb-ft.
38
Counter Electromotive Force (CEMF)
the voltage produced inside a motor that opposes the applied voltage.
39
Locked rotor current (LRC)
current through the armature when voltage is applied, but the rotor is prevented from turning.
40
Cumulatively compound
compound DC machine wherein the series and shunt coils are aligned magnetically and aid one another.
41
Differentially compound
compound DC machine wherein the series and shunt coils are misaligned magnetically and oppose one another.
42
Horsepower
the unit of measure of a motor's power output (1 horsepower = 746 watts).
43
Efficiency
The ability of a machine to convert one form of energy into another useful form of energy.
44
% Efficiency
Power outputPower input.
45
Capacitor
a device that stores energy in electrostatic form and opposes a change in voltage.
46
Dielectric
insulating material between the two conductive plates of a capacitor.
47
Plates
the two conductive metal plates of a capacitor that are separated by the dielectric.
48
Anode
the positive lead of an electronic device.
49
Cathode
the negative lead of an electronic device.
50
Capacitance
ability of a capacitor to store energy in electro-static form.
51
Farad
The unit of measure of capacitance.
52
Electrostatic charge
voltage developed by an excess or lack of electrons on an object.
53
Dielectric stress
stretching of the atoms of the dielectric due to applied voltage across the plates of a capacitor.
54
Leakage current
current that passes through the dielectric.
55
Dielectric breakdown
when current flows freely between the plates of the capacitor.
56
RC time constant
formula used to determine charge and discharge time for a capacitor (𝜏 = R x C).
57
Polarized capacitor
capacitor that is polarity-sensitive, used in DC circuits only.
58
Non-polarized capacitor
capacitor that is not polarity-sensitive, used in AC and DC circuits.
59
Right triangle
a triangle that contains a 90° angle.
60
Degree
the unit of angular measurement equal to 1/360th of a circle.
61
Hypotenuse
the longest side of a right triangle.
62
Opposite side
the side of a right triangle that is across from angle theta.
63
Adjacent side
the side of a right triangle that is beside angle theta.
64
Pythagorean theorem
the sum of the square of the sides of a right triangle equals the square of the hypotenuse.
65
Sine
angular relationship of the opposite side and hypotenuse of a right triangle.
66
Cosine
angular relationship of the adjacent side and hypotenuse of a right triangle.
67
Tangent
angular relationship of the opposite side and adjacent side of a right triangle.
68
Alternating current
electricity that changes direction periodically.
69
Transformer
device that changes one value of AC voltage into another value of AC voltage.
70
Waveform
the pattern of variations showing how a quantity changes over time.
71
Sine wave
a waveform whose shape is defined by the sine function.
72
Cycle
one complete waveform.
73
Alternation
one half of one cycle.
74
Frequency
the number of complete cycles per second.
75
Hertz (Hz)
unit of measure of frequency.
76
Instantaneous value
value of a quantity at any given moment in time.
77
Peak value
the quantity at its maximum positive or negative value.
78
Peak-to-peak value
the value of a waveform measured from one maximum to the other.
79
Average value
the value of a sine wave determined over one-half cycle.
80
RMS (Root Mean Square) value
the effective value of a sine wave.
81
Resistive load
load that contains pure resistance.
82
True power
useful power in an AC circuit expressed in watts.
83
In-phase
when voltage and current rise and fall together and cross zero at the same time.
84
Inductor
a device that stores energy in electromagnetic form and opposes a change in current.
85
Inductance
the ability of an inductor to store energy in electromagnetic form; measured in Henrys (H).
86
Phase angle
angular displacement by which voltage and current are out of phase; represented by angle theta (𝜃).
87
Impedance (Z)
total opposition to current flow in an AC circuit.
88
Reactor
an electrical device in which opposition to current flow changes with a change in frequency.
89
Inductive reactance (XL)
the opposition to current flow in an AC circuit due to inductance.
90
Capacitive reactance (XC)
the opposition to current flow in an AC circuit due to capacitance (Unit 20).
91
Apparent power (VA)
the product of the total voltage times the total current expressed in volt-amps.
92
Reactive power
power taken from and returned to an AC circuit by reactors.
93
Volt-amps Reactive (VARs)
the unit of measure of reactive power.
94
Power Factor (PF)
the ratio of true power (P) to apparent power (VA) in an AC circuit.
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