Electricity 1-7 Ch 3

Question 1

Unlike DC current, which always flows in the same direction, AC current ___________ it’s direction.

Answer 1

Periodically changes

Question 2

Practically all electricity used today is AC, what are the two reasons?

Answer 2

1. It is cheaper for power companies to produce, and distribute AC to their customers
2. AC is more versatile than DC

Question 3

Large power losses result if DC is sent over long distances. With AC, these losses are ___________.

Answer 3

Greatly reduced

Question 4

Heat loss is directly proportional to the resistance and to the square of the current. What is the formula?

Answer 4

P = I (squared) * R

Question 5

AC power can be converted to various combintations of ______ and ______.

Answer 5

Voltage
Current

Question 6

A device that converts AC power from one combination of voltage and current to another are called?

Answer 6

Transformers

Question 7

What are two sources of AC power?

Answer 7

AC Generators
Alternators

Question 8

How does an AC generator produce AC voltage?

Answer 8

Combining physical motion and magnetism

Question 9

Voltage = ___________

Answer 9

Electricity

Question 10

Angular motion is what?

Answer 10

Motion in a circle

Question 11

Waveforms can be plotted for either current or voltage. They show how the current or voltage varies with _____.
Or
Waveforms show magnitude and direction of current or voltage at every instance in _____.

Answer 11

Time

Question 12

What is the difference between AC and fluctuating DC waveforms?

Answer 12

Although they have the same shape, fluctuating DC waveforms never go below the horizontal axis.

Question 13

When an AC voltage or current goes through 360° it is said to have completed ___________.

Answer 13

One cycle

Question 14

How is frequency expressed?

Answer 14

Cycles per Second

Question 15

If the frequency of a voltage completes three cycles in one second, what is the frequency?

Answer 15

3 Hz

Question 16

Current and voltages are in phase when they both reach their maximum values and their minimum values at ______________.

Answer 16

The same time

Question 17

One full sine wave corresponds to what?

Answer 17

360°

Question 18

If two identical generators are started at the same time, turn at the same speed, and their maximum/minimum output values occur simultaneously, the two outputs are ___________.

Answer 18

In phase

Question 19

The amplitude is often referred to as the ___________.

Answer 19

Peak value

Question 20

The amplitude or peak value is the maximum ___________ and ___________ values of an AC voltage / current

Answer 20

Positive
Negative

Question 21

In a pure sign wave, the effective value is _______ time the peak value.

Answer 21

.707

Question 22

The magnitude of the current at any instant is ___________ ___________ to the magnitude of the voltage at any instant.

Answer 22

Directly proportional

Question 23

The number of cycles generated one second is called the ___________.

Answer 23

Frequency

Question 24

In AC resistive circuit, the current and voltage are ___________.

Answer 24

In-phase

Question 25

Skin factor results in higher concentration of current near the ___________ ___________ than at the conductor. Effectively, this ___________ the cross-sectional area of the conductor.

Answer 25

Conductor surface Reduces

Question 26

What are two other circuit properties that oppose the flow of AC current besides resistance? If either of them are present, AC current is ___________.

Answer 26

Inductance and Capacitance Limited

Question 27

Electric current is made up of many free ___________ moving in the _______ ___________ in a wife.

Answer 27

Elections Same direction

Question 28

The magnitude of the induced EMF is directly proportional to the strength of what three things?

Answer 28

The magnetic field The length of the conductor The speed of which the conductor moves through the magnetic field

Question 29

The strength and direction of the magnetic field around a conductor through which alternating current is flowing depends on the ___________ and ___________ of the current.

Answer 29

Magnitude Direction

Question 30

The frequency of an AC current and its amplitude determine the ___________ of the self-induced EMF.

Answer 30

Magnitude

Question 31

The magnetic field holds all the energy it has taken from the circuit until ________ ________ ________.

Answer 31

Current beings decreasing

Question 32

Each line cuts more than one loop of the conductor and generates a CEMF in every loop it cuts. The CEMF’s again add to produce a _______________.

Answer 32

Large total back EMF

Question 33

Resistor oppose all current in a circuit. They have resistance, which is abbreviated with __ . Inductors oppose changing current in a circuit. They have inductance, which is abbreviated with __.

Answer 33

R L

Question 34

________ is the property of an electrical circuit that tends to oppose any change of current through the circuit.

Answer 34

Inductance

Question 35

Inductors are also frequently called _______ or ________.

Answer 35

Chokes or coils

Question 36

For every magnetic core material, there is a point where the core becomes ________. At this point even large changes in current cannot increase flex and very little CEMF is produced.

Answer 36

Saturated

Question 37

What is the unit used for inductance?

Answer 37

henry

Question 38

Inductive reactant changes linearly with and is proportional to ________ and ________.

Answer 38

Frequency Inductance

Question 39

A CEMF act just like a resistance to ___________.

Answer 39

Limit current flow

Question 40

Sometimes dots are used to indicate the in phase terminal of the ________.

Answer 40

Two windings

Question 41

Secondary voltage lags primary current by 90° and the secondary current lags the secondary voltage by 90° , then the secondary current is ____ out of phase with the primary.

Answer 41

180°

Question 42

When secondary current in a transformer increases, the primary current automatically ________.

Answer 42

Increases

Question 43

The electrical field between the plates of the capacitor can be considered as ________.

Answer 43

Stored energy

Question 44

The unit of capacitance is the ________.

Answer 44

Farad

Question 45

The voltage applied to a capacitor is said to ____ the current through the capacitor by ___ degrees.

Answer 45

Lag 90°

Question 46

If the separation between plates and the dielectric is held constant, the capacitance of the capacitor is directly proportional to ____________________.

Answer 46

The surface area of the plates

Question 47

Apparent power is equal to _____ _____.

Answer 47

True power (In a purely resistive circuit, the power factor equals 1.0, and so the apparent power equals the true power)