BASICEC3

Question 1

______ periodically changes its direction.

Answer 1

alternating current

Basic Electricity Ch3 p.1

Question 2

Practically all of electricity used today is ac (rather than dc) because of what two reasons?

Answer 2

1. Cheaper to produce and distribute
2. more versatile

Basic Electricity Ch3 p.3

Question 3

Can DC send large amounts of electric power over long distances without large loses along the transmission line?

Answer 3

No.

Basic Electricity Ch3 p.4

Question 4

What is the equation for transmission power heat loss?

Answer 4

P = I² x R

Basic Electricity Ch3 p.5

Question 5

AC power can be converted to various combinations of ________ and ________ .

Answer 5

Voltage and Current

Basic Electricity Ch3 p.6

Question 6

The devices used to convert AC power from one combination of voltage and current to another is called…

Answer 6

a transformer

Basic Electricity Ch3 p.6

Question 7

AC power sources are called ______.

Answer 7

AC generators or alternators

Basic Electricity Ch3 p.8

Question 8

AC generators combine physical motion and magnetism to produce an ______.

Answer 8

AC voltage

Basic Electricity Ch3 p.9

Question 9

The transmission of a-c power at ______ ______ keeps power losses to a minimum.

Answer 9

low current

Basic Electricity Ch3 p.10

Question 10

_________ motion is motion in a circle.

Answer 10

Angular

Basic Electricity Ch3 p.11

Question 11

A waveform shows the ______ and ______ of the current or voltage at every instant of time.

Answer 11

magnitude, direction

Basic Electricity Ch3 p.12

Question 12

When an AC voltage or current goes through 360 degrees, it is said to have completed one _______ .

Answer 12

cycle

Basic Electricity Ch3 p.23

Question 13

____________ is expressed in cycles per second.

Answer 13

Frequency

Basic Electricity Ch3 p.23

Question 14

Phase of a waveform is used to indicate the ______ relationship between alternating voltages and currents.

Answer 14

time

Basic Electricity Ch3 p.25

Question 15

When two waveforms are in phase, it means that the peak magnitudes are reached at ______.

Answer 15

the same time

Basic Electricity Ch3 p.25

Question 16

What is another term of the maximum value that an AC current or voltage reaches?

Answer 16

amplitude or peak value

Basic Electricity Ch3 p.27

Question 17

In a pure sine wave, the effective value is ________ times the peak value.

Answer 17

.707

Basic Electricity Ch3 p.30

Question 18

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

Answer 18

directly proportional

Basic Electricity Ch3 p.34

Question 19

In DC circuits, ______ is a physical property of the conductors that opposes current flow.

Answer 19

resistance

Basic Electricity Ch3 p.37

Question 20

The skin effect, or more current flowing near the conductor surface than the center of the conductor, has the effect of ______ the cross sectional area of the conductor.

Answer 20

decreasing

Basic Electricity Ch3 p.37

Question 21

The relationship between induced emf and applied voltage that causes the current flow is such that the two voltages are always ______ out of phase.

Answer 21

180 degrees

Basic Electricity Ch3 p.39

Question 22

An electric current is made up of __________________________________.

Answer 22

many free electrons moving in the same direction in a wire.

Basic Electricity Ch3 p.43

Question 23

The magnitude of an induced emf is directly proportional to what three things?

Answer 23

1. strength of the magnetic field
2. length of the conductor
3. speed at which the conductor moves through the magnetic field

Basic Electricity Ch3 p.44

Question 24

The ______ and ______ of an AC current determine the magnitude of the self-induced emf.

Answer 24

frequency, amplitude

Basic Electricity Ch3 p.48

Question 25

During self induction, the magnetic field holds all of the energy it has taken from the circuit until the current begins \_\_\_\_\_\_.

Answer 25

decreasing Basic Electricity Ch3 p.51

Question 26

Self-induction is determined by ______ and ______ of the current.

Answer 26

amplitude, frequency Basic Electricity Ch3 p.52

Question 27

If a conductor is coiled, a ______ back emf will be produced by self-induction because the flux lines cut the conductor at more than one point.

Answer 27

greater Basic Electricity Ch3 p.52

Question 28

If either inductance or capacitance is present in an AC circuit, the current is _______ .

Answer 28

limited Basic Electricity Ch3 p.53

Question 29

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

Answer 29

inductance Basic Electricity Ch3 p.54

Question 30

Inductors are also frequently called ______ or \_\_\_\_\_\_.

Answer 30

chokes, coils Basic Electricity Ch3 p.55

Question 31

The unit of inductance is the Henry, named in honor of the American physicist \_\_\_\_\_\_, who shares the honor of the discovery of inductance with Michael Faraday.

Answer 31

Joseph Henry Basic Electricity Ch3 p.57

Question 32

If an AC circuit has only resistance, the voltage and current are ______ phase.

Answer 32

in Basic Electricity Ch3 p.63

Question 33

Inductive reactance is proportional to ______ and \_\_\_\_\_\_.

Answer 33

frequency, inductance Basic Electricity Ch3 p.65

Question 34

Sometimes dots are used to indicate ______ of the two windings.

Answer 34

the in-phase terminal Basic Electricity Ch3 p.77

Question 35

As the current in a secondary coil of a transformer increases, it reduces the _______ \_\_\_\_\_\_ in the primary, causing ______ primary current to flow.

Answer 35

back emf; more Primary and Secondary Voltage are 180 deg OutOfPhase 90 deg OOP with P I and S I Back emf is 90 deg OOP with Is Basic Electricity Ch3 p.81

Question 36

There is a special type of iron-core transformer which physically has only one winding. Functionally, though, the one winding serves as both the primary and secondary. This type of transformer is called...

Answer 36

an autotransformer Basic Electricity Ch3 p.91

Question 37

When the current has risen to a point where additional current produces only a few additional flux lines is called...

Answer 37

saturation Basic Electricity Ch3 p.98

Question 38

The electric field between the plates of a capacitor can be considered...

Answer 38

stored energy Basic Electricity Ch3 p.103

Question 39

The unit of capacitance is the \_\_\_\_\_\_.

Answer 39

Farad Basic Electricity Ch3 p.108

Question 40

If two capacitors are made with the same dielectric and the same separation between their plates, but with different sized plates, the one having plates with the ______ will have the greatest capacitance.

Answer 40

most surface area Basic Electricity Ch3 p.113

Question 41

Capacitors ______ dc current.

Answer 41

block Basic Electricity Ch3 p.118

Question 42

Capacitance is determined by what 3 factors?

Answer 42

surface area of the plates, the distance between the plates, the dielectric used Basic Electricity Ch3 p.119

Question 43

In a purely resistive circuit, the power factor equals 1.0 and so the apparent power equals the _______ \_\_\_\_\_\_\_ .

Answer 43

true power Basic Electricity Ch3 p.139