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