In a direct current (DC) circuit, the current flows in ? direction, but in an alternating
current (AC) circuit, current flows in ? direction(s).
a.
a negative / a positive
b.
a positive / a negative
c.
a single / both
d.
the forward / the reverse
The correct answer is: a single / both
An AC waveform will cross the zero axis, but a DC waveform will not cross it.
Select one:
True
False
The correct answer is 'True'.
The most common frequency in the United States is ? Hz, which means the voltage
waveform completes ? cycles in ? second(s).
a.
50 / 50 / 1
b.
50 / 50 / 50
c.
60 / 60 / 1
d.
60 / 60 / 60
The correct answer is: 60 / 60 / 1
When comparing AC to DC, it is easier to transform an AC voltage.
Select one:
True
False
The correct answer is 'True'.
Why is AC used in power distribution systems more often than DC?
I. AC can be easily transformed to raise or lower levels of voltage and current for a given
amount of power.
II. AC is easier to produce than DC.
III. AC is safer than DC.
IV. AC transformers allow very high voltage values to deliver large amounts of power at
low current levels.
a.
I. and II.
b.
I. and III.
c.
I. and IV.
d.
II. and IV.
The correct answer is: I. and IV.
In order to lower power loss by reducing the current, one must raise the ? by the same
proportion as one lowers the current to deliver the same amount of power to the user.
This is expressed mathematically as P = ? .
a.
current / I/E
b.
power / I x R
c.
resistance / E/I
d.
voltage / E x I
The correct answer is: voltage / E x I
When distributed by transmission lines, power loss is due to the ? of the wire that
generates heat in the conductor. The heat is generated as a result of ? flowing through
the conductor.
a.
diameter / power
b.
diameter / voltage
c.
length / power
d.
resistance / current
The correct answer is: resistance / current
The power loss in a conductor can be expressed mathematically as ? .
a. P = E x I
b. P = E^2/R
c. P = I^2 x R
d. P = I^2/R
The correct answer is: c. P = I^2 x R
The power loss of a transmission line can be reduced by either reducing the ? of the
wire or the amount of ? .
a.
diameter / current
b.
length / voltage
c.
resistance / current
d.
resistance / voltage
The correct answer is: resistance / current
Reducing the resistance of the wire by one-half will reduce power loss by ? , but
reducing the current by one-half will reduce the power loss by ? .
a.
25% / 50%
b.
50% / 25%
c.
50% / 50%
d.
50% / 75%
The correct answer is: 50% / 75%
AC is converted from one level of voltage for transmission and then reduced to a
different level of voltage for utilization by the end-user by using ? .
a.
converters
b.
inverters
c.
rectifiers
d.
transformers
The correct answer is: transformers
What would be the ratio of power loss of a transmission line carrying 1,000 amperes at
1,000 volts as compared to 10 amperes at 100 kilovolts? Assume a resistance of 1 ohm
on the transmission line.
a.
100 : 1
b.
1,000 : 1
c.
10,000 : 1
d.
100,000 : 1
The correct answer is: 10,000 : 1
When the current and the voltage sine waves are ? , they both have the same
frequency, crossing the reference line at the same time and going in the same direction.
a.
in-phase
b.
out-of-phase
c.
single-phase
d.
three-phase
The correct answer is: in-phase
Alternating current is used to supply over 90% of the world's electrical power
requirements.
Select one:
True
False
The correct answer is 'True'.
The variable of time in the production of electrical current has a major influence on the
effects of AC current.
Select one:
True
False
The correct answer is 'True'.
The rules of Ohm's Law, as learned in DC Theory, do not apply to AC circuits.
Select one:
True
False
The correct answer is 'False'.
The tendency of AC current to flow in the surface area of a conductor and not evenly
throughout the conductor is referred to as ? .
a.
AC effect
b.
frequency effect
c.
sine effect
d.
skin effect
The correct answer is: skin effect
Skin effect is caused by induced ? from the AC current flow, which cause the electrons
to be repelled toward the outer surface of the conductor.
a.
circular currents
b.
eddy currents
c.
negative currents
d.
positive currents
The correct answer is: eddy currents
Skin effect increases the effective resistance of the conductor.
Select one:
True
False
The correct answer is 'True'.
Skin effect is smaller at high frequencies.
Select one:
True
False
The correct answer is 'False'.
Each time the generated voltage within a generator alternator reverses polarity, the
current in an external circuit connected through slip rings to the generator alternator
? .
a.
decreases in strength
b.
increases in strength
c.
reverses direction
d.
stays the same
The correct answer is: reverses direction
In an AC generator, what changes to cause polarity changes?
a.
The armature
b.
The direction at which the conductor cuts the flux field changes as it rotates.
c.
The left hand rule
d.
The slip rings
The correct answer is: The direction at which the conductor cuts the flux field changes
as it rotates.
As a generator armature makes one full revolution, it goes through ? of mechanical
rotation.
a.
180°
b.
270°
c.
360°
d.
450°
The correct answer is: 360°
The AC voltage waveform is in the positive direction for some period of time and in the
negative direction for some period of time. What is the name given to this waveform?
a.
alternating wave
b.
inverted wave
c.
hertz wave
d.
sine wave
The correct answer is: sine wave
The plotted resulting waveform as the conductor rotates in a magnetic field follows ? .
a.
the angle of rotation
b.
the cosine of the angle of rotation
c.
the sine of the angle of rotation
d.
the tangent of the angle of rotation
The correct answer is: the sine of the angle of rotation
At what degrees on the sine wave is the voltage equal to zero?
a.
0°, 90°, 270°
b.
0°, 90°, 360°
c.
0°, 120°, 360°
d.
0°, 180°, 360°
The correct answer is: 0°, 180°, 360°
When is the voltage on an AC sine wave at the maximum positive and maximum
negative value?
a.
60°, 120°
b.
90°, 270°
c.
90°, 180°
d.
180°, 360°
The correct answer is: 90°, 270°
When a conductor cuts the magnetic flux lines at ? , the maximum voltage will be
induced into the conductor.
a.
60°
b.
90°
c.
180°
d.
360°
The correct answer is: 90°
Sine waves are so named because the voltage at any point along the wave form is equal
to the maximum, or peak, value times the ? of the angle of rotation.
a.
cosine
b.
degree
c.
sine
d.
tangent
The correct answer is: sine
A(n) ? occurs each time the AC generator finishes one complete rotation (360° travel).
a.
alternation
b.
cycle
c.
frequency
d.
hertz
The correct answer is: cycle
The measure of the number of cycles per second of the voltage produced by an AC
generator is called the ? of that voltage and is measured in ? .
a.
alternations / rpm
b.
cycles / frequency
c.
frequency / hertz
d.
period / cycles
The correct answer is: frequency / hertz
What is the frequency of a waveform that has gone through 60 positive and negative
alternations in one second?
a.
60 cycles
b.
60 hertz
c.
120 cycles
d.
120 hertz
The correct answer is: 60 hertz
The time required for one cycle is called the ? .
a.
alternation
b.
frequency
c.
hertz
d.
period
The correct answer is: period
What is the period for a frequency of 60 Hz? (Round the FINAL answer to four decimal
places of the base unit.)
Answer:
The correct answer is: 0.0167 seconds
What is the period for a frequency of 1MHz?
Answer:
The correct answer is: 1.0E-6 seconds
What is the period for a frequency of 100 Hz? (Round the FINAL answer to two decimal
places.)
Answer:
The correct answer is: 0.01 seconds
A sine wave has a maximum voltage (peak) of 144 V. What is the voltage at 45° of
rotation? (Round the FINAL answer to one decimal place.)
Answer:
The correct answer is: 101.8 V
Peak-to-peak, Peak, RMS, and Average are four forms of measurement of voltage and
current associated with sine waves.
Select one:
True
False
The correct answer is 'True'.
A measurement taken from zero to the highest value obtained in either the positive or
negative half of a sine wave would determine ? .
a.
the average value
b.
the peak-to-peak value
c.
the peak value
d.
the RMS value
The correct answer is: the peak value
The peak-to-peak value is equal to ? time(s) the peak value.
a.
0.707
b.
1.41
c.
2
d.
4
The correct answer is: 2
The current waveform shown is an example of a(n) ? .
a.
a 2-amp negative AC current
b.
a 2-amp negative DC current
c.
a 2-amp positive AC current
d.
a 2-amp positive DC current
The correct answer is: a 2-amp positive DC current
Another name for the effective value is the ? .
a.
the average value
b.
the peak-to-peak value
c.
the peak value
d.
the RMS value
The correct answer is: the RMS value
The ? is the value of AC voltage that produces the same amount of power as a like
value of DC voltage.
a.
the average value
b.
the peak-to-peak value
c.
the peak value
d.
the RMS value
The correct answer is: the RMS value
The peak voltage is measured and found to be 170 volts. What is the effective voltage?
(Round the FINAL answer to the nearest whole number.)
Answer:
The correct answer is: 120 V
The effective voltage is 480 volts. What is the peak voltage? (Round the FINAL answer to
the nearest whole number.)
Answer:
The correct answer is: 679 V
The waveforms will have the same heating effect on a resistor.
Select one:
True
False
The correct answer is 'False'.
What is the peak voltage value of an AC power source with an effective value of 50
volts? (Round the FINAL answer to the nearest whole number.)
Answer:
VAC
The correct answer is: 71
What is the peak-to-peak value of the AC voltage wave?
Answer:
The correct answer is: 100 V
If the AC voltage input to a full-wave rectifier is 100 volts peak to peak, what is the
average DC voltage value? (Round the FINAL answer to the nearest whole number.)
Answer:
The correct answer is: 32 V
When referring to values of AC voltages or currents, the letters RMS stand for Root Mean
Square.
Select one:
True
False
The correct answer is 'True'.
Give the RMS value for 120 VAC effective.
Answer:
The correct answer is: 120 V
Give the peak value for 120 VAC effective. (Round the FINAL answer to the nearest whole
number.)
Answer:
VAC
The correct answer is: 170
Give the average value for 120 VAC effective. (Round the FINAL answer to the nearest
whole number.)
Answer:
The correct answer is: 108 V
Give the peak-to-peak value for 120 VAC effective. (Round the FINAL answer to the
nearest whole number.)
Answer:
The correct answer is: 339 V
The average DC voltage value of a full-wave rectified AC sine wave can be found by
multiplying the peak value by 0.637 or by using the formula .
Select one:
True
False
The correct answer is 'True'.
Power in a circuit is the amount of work done per unit of ? .
a.
current
b.
time
c.
voltage
d.
wattage
The correct answer is: time