Unit 16 - Alternating Current

The output voltage of a generator depends upon the _____.
number of turns of wire
strength of the magnetic field
speed at which the coil rotates
all of these

all of these

When a magnetic field moves through a coil of wire, the lines of force of the magnetic field cause the electrons in the wire to flow in a specific direction. When the magnetic field moves in the opposite direction, electrons in the wire flow in the opposite direction.
TRUE
FALSE

TRUE

Effective ac voltage or effective ac current is the equivalent value of dc voltage or dc current that would produce the same amount of heat in a resistor.
TRUE
FALSE

TRUE

_____ is the value of the voltage or current at a given moment of time.
Peak
Root-mean-square
Effective
Instantaneous

Instantaneous

If the voltage waveform finishes before the current waveform, the voltage is said to "_____" the current waveform.
lead
lag
be in-phase with
none of these

lead

The rerm "phase" is used to indicate the time or degree relationship between two waveforms, such as voltage-to-current or voltage-to-voltage.
TRUE
FALSE

TRUE

A nonsinusoidal waveform is created when _____ loads distort the voltage and current sine wave.
linear
resistive
inductive
nonlinear

nonlinear

In a purely resistive ac circuit, the current and voltage are _____. This means that they both reach their zero and peak values at the same time.
in-phase
out-of-phase
a or b
none of these

in-phase

The effective value is equal to the peak value _____.
times 0.707
times 1.41
divided by 1.41
times 0.58

times 0.707

_____ describes the steps necessary to determine the effective voltage or current value.
Peak
Root-mean-square
Instantaneous
none of these
C

Root-mean-square

_____ is the maximum value that ac current or voltage reaches, both for positive and negative polarity.
Peak
Root-mean-square
Instantaneous
none of these

Peak

The combination of alternating-current and direct-current waveforms results in a _____ waveform.
nonsinusoidal
nonsymmetrical
sine
any of these

nonsymmetrical

The number of complete waveforms in one second is called the "frequency." Frequency is expressed as "_____" or "cycles per second."
degrees
a sine wave
phase
Hertz

Hertz

Phase differences are expressed in _____.
sine waves
phases
Hertz
degrees

degrees

In ac generators that produce large quantities of electricity, the conductor coils are stationary and the magnetic field revolves within the coils.
TRUE
FALSE

TRUE

A three-phase generator has each of its windings out-of-phase with each other by _____.
90°
120°
180°
360°

120

The peak value is equal to the effective value _____.
times 0.707
times 1.41
divided by 2
times 0.58

times 1.41

A waveform image is used to display the level and direction of current, but not voltage.
TRUE
FALSE

FALSE

Phase differences are expressed in degrees. One full waveform is equal to _____.
90°
120°
180°
360°

360

Alternating current is primarily used because it can be transmitted inexpensively.
TRUE
FALSE

TRUE

When the current waveform finishes before the voltage waveform, the voltage "_____" the current waveform.
leads
lags
is in-phase with
none of these

lags

A simple ac generator consists of a loop of wire rotating across the lines of force between the opposite poles of a magnet.
TRUE
FALSE

TRUE

The movement of electrons themselves does not produce any useful work. It's the effects that the moving electrons have on the loads they flow through that are important.
TRUE
FALSE

TRUE

When describing the relationship between voltage and current, the reference waveform is always _____.
current
resistance
voltage
none of these

voltage

The waveform for ac circuits displays the level and direction of the current and voltage for every instant of time for one full revolution of the rotor.
TRUE
FALSE

TRUE

The _____ wave is a waveform that is symmetrical with positive above and negative below the zero reference level.
nonsinusoidal
nonsymmetrical
sine
any of these

sine