Alternating Current- Introduction to Alternating Current (AC)

Alternating Current (AC) The electromagnetic wave seen in the Figure on an oscilloscope is an electrical representation of alternating current and is one of the most useful and enigmatic phenomena known to man. Every day, waveforms like this one are emitted by radio, television, telephone, and other communication device antennas all over the world.

The antenna’s alternating current (AC) is a primary man-made source of electromagnetic waves. Alternating currents amplified by various electronic circuits and added to antennas to radiate across space and relay information are used to generate words, audio, TV images, and other sounds.

This first chapter presents an operational description for ac with comparisons of ac and dc waveforms; theorizes and illustrates the generation of an ac waveform, and introduces the time and frequency relationships of ac waveforms.

AC Voltage and Current

Definition of alternating current

The abbreviation for alternating current is AC. An alternating current is a type of electrical current that changes in magnitude as well as direction. The term magnitude refers to the quantitative meaning of a circuit’s current, or how much current is flowing. The term direction denotes the direction in which current flows in a circuit.

Generating an AC Waveform

Generating an AC Waveform

The figure displays a basic dc circuit that can be used to simulate alternating current. A variable dc power supply, a resistor, and a galvanometer make up the circuit. The galvanometer is an ammeter with a zero ampere centre scale value.

If current flows counter-clockwise in the circuit, the meter needle will deflect to the left. The meter needle will deflect to the right if the current flows clockwise.

Electron current flow will be counter-clockwise in the circuit configuration depicted in Figure. As the power supply voltage is raised, the galvanometer needle will deflect to the left before it reaches a maximum current value. The current flow in the circuit decreases to zero amperes as the voltage is reduced to zero volts.

As a result, a current flow of varying magnitude has been expected. This satisfies one of the two alternating current requirements. To satisfy the other criteria, a change of direction, the battery’s polarity can be reversed, as seen in Figure. Take note that the current is now flowing clockwise.

The galvanometer needle deflects to the right to some optimum value as the power supply voltage is increased. As the voltage is reduced to zero volts, the current flow in the circuit is reduced to zero amperes.

Plotting an AC Waveform

Plotting an AC Waveform

This alternating current can be graphically depicted, as shown in Figure 1.5. The axes of this graph are set up to plot current versus time. The horizontal, or X-axis, axis of time is plotted.

The vertical, or Y-axis, the axis of current is plotted. The vertical axis is divided into positive (+) and negative (-) present values above and below the X-axis. This polarity classification is clearly used to distinguish the direction of current flow.

Current flow in the counter-clockwise direction will be designated as positive current in this application, while current flow in the opposite, clockwise direction, will be designated as negative current. The polarity and direction are chosen at random.


If there is current flow in a circuit, there must be a potential difference, or voltage difference. As shown in the diagrams, the voltage, E, that generates the alternating current must change in the same way as the current.

To allow the current to change direction, the polarity of the voltage must change. An alternating voltage (ac voltage) is a voltage that induces an alternating current.

Also Read: Parallel Plate Capacitor: Electric field, Equation, Capacitance Explained

Summary of DC and AC Voltages and Currents

The distinction between dc and alternating current voltages and currents can now be summarised. A direct current (DC) is a current that flows in just one direction. Its amplitude can change, and if it does, it is referred to as pulsating dc.

A direct current voltage is one that generates a direct current. Its polarity does not change. AC stands for alternating current, which is a current that varies in both magnitude and direction.

An alternating current voltage (AC voltage) is a voltage that induces an alternating current. Its amplitude and polarity change. The magnitude or value of an alternating current voltage is referred to as its amplitude.

Also Read: what is a flux capacitor: Real life, Uses & Video Explained

Contrasting DC and AC Waveforms

Contrasting DC and AC Waveforms

A comparison of various types of dc and ac voltage waveforms should help you understand the distinctions between the two. Since it does not change polarity, the waveform in Figure an is a dc waveform. It is worth noting that the amplitude remains constant.

As a consequence of a fixed value of dc voltage, the plot of current versus time in a circuit with the voltage of Figure and applied will also be a constant value.

Figure b depicts a dc waveform as well. It has the opposite polarity as the waveform in Figure a, but it also does not change in amplitude.

Contrasting DC and AC graph

The waveform in Figure a is a dc waveform and it is a pulsating waveform. The entire waveform is in the positive portion of the graph and never crosses the X-axis.

If the line graph had crossed the X-axis into the opposite half of the graph, and if this voltage were applied to a circuit, then it would have caused the circuit current to change direction and it would no longer be considered a dc voltage. This is the most important point in distinguishing between dc and ac waveforms.

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AC Waveform

Now that the differences between dc and ac have been determined and a definition of ac has been developed, we can discuss how alternating current is generated. By periodically reversing the connections from a dc power source to the circuit, an alternating current can be generated. This, however, is not feasible.

A standard household alternating current, for example, reverses polarity 60 times per second when driven by a 110 VAC, 60-hertz source voltage. It is nearly impossible to reverse the connections to a dc power source 60 times per second. An alternating current generator is a more practical way to produce alternating current.

Also Read: Colpitts Oscillator: Working, Circuit, frequency derivation

AC Generator

An ac generator is a system that produces alternating current voltage by spinning a conductor material loop through a magnetic field. Understanding the function of an alternating current generator necessitates a clear understanding of magnetic theory.

Magnetic Lines of Force

Magnetic Lines of Force

It is well understood that magnets have north and south poles and that they attract other magnetic materials. A magnetic field occurs between the two poles of two magnets when they are brought close together.

If these two poles are opposite, with one being a north pole and the other a south pole, the flux lines would flow from the north pole to the south pole, as shown in the diagram in Figure. The magnetic field between the two poles becomes greater as the magnets get stronger.

Iron filings, as shown in Figure, can be used to demonstrate the presence of flux lines between the north and south magnetic poles. The magnets are placed on the table with their north and south poles facing each other, a sheet of plexiglass is draped over them, and iron filings are sprinkled on top.

Since iron fillings are magnetic, they align themselves with the flux lines of the magnetic field. These lines are important because they illustrate how to generate ac.

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Direct current vs Alternating current

As useful and simple as direct current is, it is not the only type of electricity in use. Certain electricity sources generate voltages that alternate in polarity, reversing positive and negative over time. This “kind” of electricity is known as Alternating Current because it can turn polarity as a voltage or as a current switching direction back and forth (AC).

Whereas the familiar battery symbol is used to represent any DC voltage source, the circle with the wavy line within is used to represent any AC voltage source. One might wonder why someone would bother with AC in the first place. Real, in some situations, AC has no practical advantage over DC.

The polarity or direction of current is irrelevant in applications where electricity is used to dissipate energy in the form of heat, as long as there is enough voltage and current to the load to provide the desired heat (power dissipation).

However, with AC, it is possible to create much more powerful electric generators, engines, and power distribution systems than with DC, and hence AC is widely used in high power applications around the world.

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Why is AC used over DC

The main advantage of AC electricity over DC electricity is that AC voltages can be easily converted to higher or lower voltage levels, while DC voltages are difficult to do. AC electricity has an advantage over DC since high voltages are more effective at transmitting electricity over long distances.

What is AC or DC current

AC and DC both define different forms of current flow in a circuit. The electric charge (current) in direct current (DC) only flows in one direction. Electric charge in alternating current (AC), on the other hand, alternates direction on a regular basis.

What is alternating current used for

The flow of charge that changes direction on a regular basis is referred to as alternating current. As a consequence, the voltage level reverses in lockstep with the current. AC is used to fuel residences, businesses, and other structures.

How does AC current work

A loop of wire is spun rapidly inside a magnetic field in an alternator. This causes an electric current to flow through the cable…. Since the current shifts direction on a regular basis, the voltage in an alternating current circuit often reverses on a regular basis.

Why DC current is not used in homes

DC is more lethal than AC with the same voltage because it is more difficult to let go of if touched because the voltage does not pass through zero. With DC, electrolytic corrosion is more of a concern. DC arcs do not “quench” as quickly as AC arcs.

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