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Module 4, Lesson 3 > ITEC 220 Test #3 > Flashcards

ITEC 220 Test #3 Flashcards

1
Q

Cycle

A

The complete sequence of values of a repetitive voltage or current

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2
Q

Waveform

A

A graph showing the variations of the voltage and current with respect to time

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3
Q

Period

A

The time of one complete cycle

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4
Q

Periodic waveform

A

A graph of a wave which repeats itself every period

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5
Q

Time duration (t)

A

The length of time needed to complete a cycle

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6
Q

Frequency

A

The number of cycles per unit of time

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7
Q

Hertz (Hz)

A

Unit of frequency measurement meaning cycles per second

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8
Q

Sinusoidal waveform

A

Any waveform that can be expressed as a sum of sine functions in respect to time

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9
Q

Alternation

A

A way of describing the state of a voltage or current which changes polarity periodically

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10
Q

Radian

A

Unit of angular measurement in which the arc of the angle on the circle is equal to the circles radius

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11
Q

Sine wave

A

A voltage or current whose waveform can be expressed by a single sine function in respect to time

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12
Q

Instantaneous voltage

A

The voltage present at a particular instant

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13
Q

Define the period as applied to an AC waveform

A

The time of one complete cycle

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14
Q

Define frequency as applied to an AC waveform

A

The number of cycles per unit of time

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15
Q

How man alternations are there in one cycle

A

2

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16
Q

How many radians are there in an angle of 180

A

3.14 (pi)

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17
Q

What is the peak value of a sine wave with a peak-to-peak voltage of 120 volts AC

A

60 HAC

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18
Q

What is the peak-to-peak value of a sine wave with a peak voltage of 120 volts AC

A

240 HAC

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19
Q

What is the average value (in volts) of a complete sine wave with equal amplitude positive and negative alternations

A

0

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20
Q

If the positive and negative alternations of a waveform are unequal in amplitude, is the waveform sinusoidal

A

No

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21
Q

AC voltages and currents are expressed in

A

RMS

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22
Q

The AC voltage of the power lines in our homes are rated for

A

110-120 volts

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23
Q

Average

A

Difference between the positive and negative peaks

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24
Q

The AC volts scale of a multimeter usually indicates

A

RMS voltages

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25
Can an oscilloscope be used to measure RMS voltage and peak-to-peak voltage
Yes
26
Inductance
The property of a conductor that opposes a change in a circuit
27
Counter EMF
The effect that an inductor produces an opposing voltage to the applied voltage as the magnetic field changes with the applied voltage
28
Self-induction
Induction of an electromotive force in a coil by varying the current in the coil.
29
`Mutual induction
Induction of an electromotive force in a coil by a varying current in another coil which is magnetically coupled to the first coil
30
Inductor
An electrical unit that exhibits inductance. Sometimes called a coil
31
Henry
Basic unit of measure of inductance
32
The letter symbol for inductance
L
33
Reactance
An opposition of current flow in an AC current
34
When AC is used, the voltage and current change
continuously
35
The counter EMF developed across a coil, to which AC is applied is directly
Proportional to the frequency changes in AC voltages
36
Inductive reactance
The opposition an inductor offers to current flow in an AC circuit
37
Angular velocity
The rate for expressing a change in radians per unit of time. It is equal to 2(3.14)(f), where f is expressed in Hertz
38
The counter EMF developed across a coil, to which AC is applied, is directly
Proportional to the inductance in a coil
39
Inductive reactance of a coil is directly
Proportional to frequency to the inductance of the coil
40
Phase angle
The angular difference between two waveforms
41
Impedance
The vector sum of resistance and reactance
42
Counter EMF is developed in a coil only when DC is applied, T or F
False
43
Increasing the frequency of the AC source (increases, decreases) the counter EMF coil
Increases
44
1 kilohertz equals
1000 hertz
45
1 megahertz equals
1,000,000 hertz
46
Current method
A method of calculating the impedance of a parallel circuit by first calculating the branch currents, adding the branch currents vectorially, and determining the impedance by Ohm's law
47
Mutual coupling
The interaction produced by two coils which share the same magnetic filed
48
Mutual inductance
The inductance that modifies the total inductance of two coils which are connected together and share the same magnetic filed
49
In a series RL circuit, the voltage must be added (arithmetically, vectorially)
Vectorially
50
The impedance of a series RL circuit is less than the sum of R plus XL
True
51
In a parallel circuit, what is the same in all components
Voltage
52
In parallel RL circuits, the resistance value is increases. How is total circuit current affected
The total current decreases
53
What are the 2 applications of inductors
1. Oppose changes of current through them 2. Inductive reactance is directly proportional to the frequency of the source voltage
54
Transformer
An electrical device that transfers electrical energy from one circuit into another by electromagnetic induction
55
Mutual coupling (transformers)
The method by which a changing current in one coil causes a voltage to be induced in another coil
56
Primary winding
Portion of the transformer to which the input is applied
57
Secondary winding
Portion of the transformer from which the output is obtained
58
Why is soft iron preferred over steel as a core material
It does not retain magnetism
59
Turns ratio
The ratio number of turns of the secondary winding divided by the number of turns of the primary winding
60
More primary turns
Step-down transformer
61
More secondary turns
Step-up transformer
62
Eddy currents
Are currents that are produced by the voltages induced into the core of a transformer
63
Hysteresis
The delay in magnetism caused by extra energy and time required to change the magnetization of the minute molecular magnets in the core
64
Core loss
The total losses in the core due to eddy currents and hysteresis
65
I2R loss
The loss of energy due to the resistance of the copper wire
66
Transformer hum
The vibration caused by the movement of the plates of the transformer core
67
Flux leakage
A loss of magnetic flux
68
Core Saturation
A condition where the core will accept no more magnetic flux
69
Copper losses in a transformer could be decreased by
A higher quality copper
70
Laminating an iron core decreases what
Eddy current losses
71
Why are transformers used in long-dsitance power transmissions systems
The applied voltages can be increased or decreased
72
List several additional uses of transformers
Computers, cellphones, substances, and instrument transformers

Module 4, Lesson 3 (18 decks)

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