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Electrical Circuits Electrical Circuits
Page 2


Electrical Circuits Electrical Circuits
2
AC Fundamentals
Ø Previously you learned that DC sources have ?xed polarities and constant
magnitudes and thus produce currents with constant value and unchanging
direction
Ø In contrast, the voltages of ac sources alternate in polarity and vary in
magnitude and thus produce currents that vary in magnitude and alternate in
direction.
Page 3


Electrical Circuits Electrical Circuits
2
AC Fundamentals
Ø Previously you learned that DC sources have ?xed polarities and constant
magnitudes and thus produce currents with constant value and unchanging
direction
Ø In contrast, the voltages of ac sources alternate in polarity and vary in
magnitude and thus produce currents that vary in magnitude and alternate in
direction.
3
AC Fundamentals
Ø Sinusoidal ac Voltage
One complete variation is referred to as a cycle.
Starting  at  zero,
the  voltage increases  to  a  positive  peak  amplitude,
decreases  to  zero,
changes  polarity,
increases to a negative peak amplitude,
then returns again to zero.
Ø Since the waveform repeats itself at regular intervals, it is called a periodic signal.
Ø Symbol for an ac Voltage Source
Lowercase letter e is used
to indicate that the voltage varies with time.
Page 4


Electrical Circuits Electrical Circuits
2
AC Fundamentals
Ø Previously you learned that DC sources have ?xed polarities and constant
magnitudes and thus produce currents with constant value and unchanging
direction
Ø In contrast, the voltages of ac sources alternate in polarity and vary in
magnitude and thus produce currents that vary in magnitude and alternate in
direction.
3
AC Fundamentals
Ø Sinusoidal ac Voltage
One complete variation is referred to as a cycle.
Starting  at  zero,
the  voltage increases  to  a  positive  peak  amplitude,
decreases  to  zero,
changes  polarity,
increases to a negative peak amplitude,
then returns again to zero.
Ø Since the waveform repeats itself at regular intervals, it is called a periodic signal.
Ø Symbol for an ac Voltage Source
Lowercase letter e is used
to indicate that the voltage varies with time.
4
Sinusoidal ac Current
Ø During the ?rst half-cycle, the
source voltage is positive
Ø Therefore, the current is in the
clockwise direction.
Ø During the second half-cycle, the
voltage polarity reverses
Ø Therefore, the current is in the
counterclockwise direction.
Ø Since current is proportional to voltage, its
shape is also sinusoidal
Page 5


Electrical Circuits Electrical Circuits
2
AC Fundamentals
Ø Previously you learned that DC sources have ?xed polarities and constant
magnitudes and thus produce currents with constant value and unchanging
direction
Ø In contrast, the voltages of ac sources alternate in polarity and vary in
magnitude and thus produce currents that vary in magnitude and alternate in
direction.
3
AC Fundamentals
Ø Sinusoidal ac Voltage
One complete variation is referred to as a cycle.
Starting  at  zero,
the  voltage increases  to  a  positive  peak  amplitude,
decreases  to  zero,
changes  polarity,
increases to a negative peak amplitude,
then returns again to zero.
Ø Since the waveform repeats itself at regular intervals, it is called a periodic signal.
Ø Symbol for an ac Voltage Source
Lowercase letter e is used
to indicate that the voltage varies with time.
4
Sinusoidal ac Current
Ø During the ?rst half-cycle, the
source voltage is positive
Ø Therefore, the current is in the
clockwise direction.
Ø During the second half-cycle, the
voltage polarity reverses
Ø Therefore, the current is in the
counterclockwise direction.
Ø Since current is proportional to voltage, its
shape is also sinusoidal
5
Generating ac Voltages (Method A)
Ø One  way  to  generate  an  ac  voltage  is  to  rotate  a  coil  of  wire  at  constant
angular velocity in a ?xed magnetic ?eld
Ø The magnitude of the resulting voltage is proportional to the rate at which ?ux
lines are cut
Ø its polarity is dependent on the direction the coil sides move through the ?eld.
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FAQs on PPT: Single-Phase AC Circuits - Basic Electrical Technology - Electrical Engineering (EE)

1. What is a single-phase AC circuit?
Ans. A single-phase AC circuit is an electrical circuit that carries alternating current (AC) with only one phase. It is commonly used in residential and small commercial applications to power lighting, appliances, and other electrical devices.
2. How does a single-phase AC circuit differ from a three-phase AC circuit?
Ans. The main difference between a single-phase AC circuit and a three-phase AC circuit is the number of phases. A single-phase circuit has only one phase, while a three-phase circuit has three phases. Three-phase circuits are typically used in industrial, commercial, and larger residential applications to provide higher power capacity and better efficiency.
3. What are the advantages of using a single-phase AC circuit?
Ans. Some advantages of using a single-phase AC circuit include its simplicity, lower installation costs, and compatibility with most electrical devices found in homes and small businesses. Single-phase circuits are also easier to understand and troubleshoot compared to three-phase circuits.
4. Can a single-phase AC circuit be converted to a three-phase AC circuit?
Ans. Yes, it is possible to convert a single-phase AC circuit to a three-phase AC circuit using certain electrical equipment such as phase converters. However, the conversion process can be complex and may require professional assistance. It is important to carefully evaluate the power requirements and compatibility of the electrical devices before attempting such a conversion.
5. How does the voltage in a single-phase AC circuit fluctuate over time?
Ans. In a single-phase AC circuit, the voltage fluctuates sinusoidally with time. The voltage waveform follows a pattern known as a sine wave, where the voltage rises to a maximum value, then decreases to zero, and finally reaches a minimum value before rising again. These voltage fluctuations occur at a frequency of 50 or 60 Hz, depending on the country's electrical system.
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