AC SYSTEMS, LEVEL 1 - 3RD ED.
LESSON 3 QUESTIONS AND ANSWERS
WITH SOLUTTIONS 2024
In a direct current (DC) circuit, the current flows in ? direction, but in an alternating current (AC) circuit,
current flows in ? direction(s). - ANSWER a single / both
An AC waveform will cross the zero axis, but a DC waveform will not cross it. - ANSWER True
The most common frequency in the United States is ? Hz, which means the voltage waveform completes
? cycles in ? second(s). - ANSWER / 1
When comparing AC to DC, it is easier to transform an AC voltage. - ANSWER True
Why is AC used in power distribution systems more often than DC? - ANSWER I. AC can be easily
transformed to raise or lower levels of voltage and current for a given amount of power.
IV. AC transformers allow very high voltage values to deliver large amounts of power at low current
levels.
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 = ? . - ANSWER 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. - ANSWER resistance /
current
The power loss in a conductor can be expressed mathematically as ?. - ANSWER P = I² x R
The power loss of a transmission line can be reduced by either reducing the ? of the wire or the amount
of ? . - ANSWER 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 ? . - ANSWER 50% / 75%
P = I² x R
160 = 4² x 10 (base equation)
80 = 4² x 5 (if resistance is reduced)
40 = 2² x 10 (if current is reduced)
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 ? . - ANSWER 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 kV? Assume a resistance of 1 ohm on the transmission line. - ANSWER
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. - ANSWER in-phase
Alternating current is used to supply over 90% of the world's electrical power requirements. - ANSWER
True
The variable of time in the production of electrical current has a major influence on the effects of AC
current. - ANSWER True
The rules of Ohm's Law, as learned in DC Theory, do not apply to AC circuits. - ANSWER 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 ? . - ANSWER 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. - ANSWER Eddy Currents
LESSON 3 QUESTIONS AND ANSWERS
WITH SOLUTTIONS 2024
In a direct current (DC) circuit, the current flows in ? direction, but in an alternating current (AC) circuit,
current flows in ? direction(s). - ANSWER a single / both
An AC waveform will cross the zero axis, but a DC waveform will not cross it. - ANSWER True
The most common frequency in the United States is ? Hz, which means the voltage waveform completes
? cycles in ? second(s). - ANSWER / 1
When comparing AC to DC, it is easier to transform an AC voltage. - ANSWER True
Why is AC used in power distribution systems more often than DC? - ANSWER I. AC can be easily
transformed to raise or lower levels of voltage and current for a given amount of power.
IV. AC transformers allow very high voltage values to deliver large amounts of power at low current
levels.
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 = ? . - ANSWER 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. - ANSWER resistance /
current
The power loss in a conductor can be expressed mathematically as ?. - ANSWER P = I² x R
The power loss of a transmission line can be reduced by either reducing the ? of the wire or the amount
of ? . - ANSWER 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 ? . - ANSWER 50% / 75%
P = I² x R
160 = 4² x 10 (base equation)
80 = 4² x 5 (if resistance is reduced)
40 = 2² x 10 (if current is reduced)
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 ? . - ANSWER 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 kV? Assume a resistance of 1 ohm on the transmission line. - ANSWER
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. - ANSWER in-phase
Alternating current is used to supply over 90% of the world's electrical power requirements. - ANSWER
True
The variable of time in the production of electrical current has a major influence on the effects of AC
current. - ANSWER True
The rules of Ohm's Law, as learned in DC Theory, do not apply to AC circuits. - ANSWER 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 ? . - ANSWER 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. - ANSWER Eddy Currents
