ITEC 220 Test #3 Flashcards Preview

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

Flashcards in ITEC 220 Test #3 Deck (72):
1

Cycle

The complete sequence of values of a repetitive voltage or current

2

Waveform

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

3

Period

The time of one complete cycle

4

Periodic waveform

A graph of a wave which repeats itself every period

5

Time duration (t)

The length of time needed to complete a cycle

6

Frequency

The number of cycles per unit of time

7

Hertz (Hz)

Unit of frequency measurement meaning cycles per second

8

Sinusoidal waveform

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

9

Alternation

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

10

Radian

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

11

Sine wave

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

12

Instantaneous voltage

The voltage present at a particular instant

13

Define the period as applied to an AC waveform

The time of one complete cycle

14

Define frequency as applied to an AC waveform

The number of cycles per unit of time

15

How man alternations are there in one cycle

2

16

How many radians are there in an angle of 180

3.14 (pi)

17

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

60 HAC

18

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

240 HAC

19

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

0

20

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

No

21

AC voltages and currents are expressed in

RMS

22

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

110-120 volts

23

Average

Difference between the positive and negative peaks

24

The AC volts scale of a multimeter usually indicates

RMS voltages

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