Alternating Current: Definition, Examples, Benefits, and Dangers

Alternating Current – The application of an alternating current circuit can actually be seen in the workings of a power generator which is commonly used when the electricity at home is out. Alternating current circuit is also divided into several types. Previously, first identify what an electric current is. Electric current or electric current is a flow that occurs due to the amount of electric charge flowing from one point to another, in a circuit per unit time.

In the book Modeling for Electrical Circuits by AM Shiddiq Yunus et al., based on the direction of flow, electric current is divided into two types, namely direct current and alternating current. Direct current or also known as direct current (DC) flows from a high potential point to a low potential point. Meanwhile, alternating current ( AC) flows arbitrarily and follows the timeline.

Alternating current is usually used for electronic equipment. To go deeper, here are the definitions and types of alternating current circuits quoted from various sources.

Definition of Alternating Current

Alternating current is an electric current that has the direction of the current changing back and forth. The nature of alternating current differs from direct current in that the direction of the current does not change with time. The waveform of this current is usually in the form of a sinusoidal wave which allows energy to flow efficiently. The current can also flow in triangular or rectangular waveforms.

Alternating current (green line) and direct current (red line) diagram.

In general, the distribution of alternating current electricity from power sources to offices or people’s homes. This current is also transmitted as radio or audio signals that are carried through the cable. In these applications, the most important primary objective is the retrieval of the information modulated or encoded in the alternating current signal.

History of the Use of Alternating Current

In 1835, Hippolyte Pixii built the first alternating current generator. Pixii makes the tool with a rotating magnet. Until 1822, the alternating current generator made by Pixii did not attract the attention of scientists because the design of the power plant was focused on direct current power generation.

The study of alternating current only started in 1882 with rapid development. Various inventions related to alternating current electricity were made by electrical scientists such as Thomas Alva Edison and Nikola Tesla. Sebastian Ferranti and Lord Kelvin ultimately created the earliest alternating current and transformer power generation technologies.

The first alternating current system was constructed in Great Barrington, Massachusetts by William Stanley. Making this alternating current system is supported by Westinghouse. At the same time, Nikola Tesla also started selling alternating current electrical system designs in New York.

By that time, New York had adopted a direct current electrical system so sales of alternating current systems failed. In 1887, CS Bradley made a 3-phase alternating current generator which is a tool that makes alternating electric current more efficient so that it is used today. In 1900, 3-phase alternating generator has become the basic principle source of electric power in the world.

The use of alternating current has experienced rapid technological developments as well as the convenience of alternating current electricity in electric power transmission and distribution of electric power, making alternating current a competitor of direct current. The distribution of direct current electricity which began at the end of the 19th century AD by Thomas Alva Edison was later replaced by alternating current.

1. Source

Alternating current can be generated using a low-frequency electric generator. The frequency of alternating current electricity generation is not more than 1 kHz. The principle of alternating current generation is carried out by utilizing the principle of electromagnetism. The two poles of the magnetic field are placed in a coil with a conductor wound. The magnetic field and the resulting alternating electric current strength are based on the surface area of ​​the coil.

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2. Shape

City lights as seen from moving camera. Alternating current electricity causes the lights to flicker which makes visible lines become spots.

The sine wave is the simplest form of alternating current. Current in the form of a sine wave is generated by various types of power plants that use a turbine as the generator rotor drive. These types of power plants include hydroelectric power plants, coal-fired power plants, wind power plants, and nuclear power plants.

3. Unit of Measurement

The unit of measurement for electric current used internationally is the Ampere. This unit standard was first established in 1893 along with the Ohm unit and the Volt unit. The end result of the international meeting is the determination of the value of the international Ampere unit.

The international amperage is defined as the constant amount of electric current that is capable of passing through an aqueous solution of silver nitrate according to standard specifications. Silver deposition is carried out at a speed of 0.001118 grams per second. On January 1, 1948 a new standard was set which has become the absolute standard to this day. In absolute standards it is determined that one international Ampere is equal to the value of 0.99835 absolute amperes.

Alternating Current Formulation

1. Mains Voltage

The existence of alternating current means that the electric voltage is also alternating. Alternating voltage can be represented by this formula:



  • is the peak voltage (unit: volts).
  • is the corner frequency (unit: radians per second).
  • The angular frequency can be related to the usual frequency, (unit = hertz), which is represented by revolutions per second, using the formula .
  •  is the time (unit: second).

2. Electrical Power

The relationship between electric power and alternating voltage can be represented by:

where is the load resistance.

3. Vibration Power

Using trigonometric identities, the oscillation energy is doubled in frequency by electrical pressure.

4. Average Voltage

  • For sinusoidal voltage:
The factor is the crest factor, which is different in different functions.
  • For triangle waveforms:
  • For square waveforms:
  • For a basic waveform with a period  :

Alternating Current Frequency

Electrical system frequencies vary in different countries, but are usually in the range of 50-60 Hertz. Some countries like Japan have two different electricity frequencies, namely 50 Hz and 60 Hz, depending on the power plant used.

Frequencies ranging from 50–60 Hz were chosen for quite reasonable reasons. Low-frequency electric current makes electricity users with electric motors easier. Especially with applications related to traction from the commutator, such as in the case of railroads. But by using a low frequency, you will see flickering in the lights which is very annoying, especially in incandescent lamps.

Practical Applications of Alternating Current

1. Alternating Current Electric Motors

Alternating current electric motors use an electric current which has a working principle that reverses its direction regularly at a certain time. The basic parts of this electric motor are the stator and rotor. The stator is where the rotor rotates, while the rotor is an electrical component that rotates to rotate the motor shaft.

Alternating current electric motors overcome the weakness of direct current motors, namely the speed that is difficult to control. Alternating current motors are equipped with a drive called variable frequency which functions to improve speed control while reducing the use of electric power.

2. Induction Motors

Modern electrical systems started when induction motors used alternating current. The use of alternating current in an induction motor was first made by Nikola Tesla. Alternating current is the driving force of the rotor in an alternating current motor. The rotor is located inside the motor and is the rotating part. Rotor rotation occurs because of the torque acting on its axis. Torque is generated by a rotating magnetic field due to alternating current.

Alternating current electric motors have been used in household electrical appliances such as washing machines, fans and air conditioners. In industrial motion control processes, induction motors are the most commonly used electric motors. Alternating current induction motors have a simple design with low maintenance levels. The source of electric voltage to do work on electric motors can be obtained directly through an alternating current power source that is available in the building’s electrical installation.

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3. Synchronous Motors

Synchronous motors are included in electric motors that use an alternating electric current source. The way the motor works starts from applying voltage to the stator coil with a 3-phase system. The application of voltage produces a rotating magnetic flux and creates an electromotive force on the stator coil. The continuous rotation produces a rotating magnetic flux which cuts the coil every time.

The rotating flux generated by the alternating current is not entirely generated in the stator coil. A leakage flux arises in the stator coil which is expressed by the armature resistance and armature reactance. The rotor coil is located between the north magnetic pole and the south magnetic pole so that it has a magnetic flux. The two magnetic fluxes will interact with each other and cause the rotor to rotate. The rotation of the rotor is equal to the speed of the rotating magnetic flux from the stator.

4. Transformer

A transformer or transformer is a tool that has a working principle of being able to convert from alternating current to direct current by transferring alternating current electric power between two or more coils of wire through electromagnetic induction. The principle of this transformer makes the transformer a tool that has advantages over other tools.

5. Alternating Current Motor Control

In alternating current motor control, the role of the transformer is to reduce the voltage at the motor terminals during the acceleration period, this method is called starting of the autotransformer. Alternating current motors require a very large initial current so we need a way for this motor to work effectively and efficiently. During starting with reduced voltage, the motor is connected to the taps on the autotransformer.

The low starting voltage makes the motor draw less amperage and produce less torque than if it were connected directly to mains voltage. The voltage transfer can be regulated in a relay if the transfer experience a reduction in the total voltage voltage. A current-sensitive relay may be used to control the displacement to obtain limited current acceleration.

6. Transformer Structure

Alternating Current Danger

Alternating current with a rating of up to 10 Amperes cannot harm humans as long as it does not touch and flow to the body. On the other hand, this current, which ranges from 10 to 100 milliamperes and has a low frequency, can cause death if it comes in direct contact with the human body. The frequency threshold that is not harmful to the human body is 10 5 Hz. The heat generated by the electric current can also penetrate several millimeters deep into the surface of the skin and damage it. High-frequency currents can generate heat which can damage the internal organs of the body.

Example Question About Alternating Current

In order to go deeper into the material above, the following are examples of questions and discussion taken from the book Electrical Voltage Sources: History, Working Principles, and Their Application by Trigonggo to the site .

Thus the discussion regarding the meaning of alternating current, examples, benefits, and dangers that need to be known. Want to learn more about natural science with the integration of the latest technology? sinaumedia believes that the power of an integrated system ensures that every student is developed and educated holistically – from academics to character building and cultivating a lifelong love of learning.

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  • Abdullah, Mirajuddin (2017). Basic Physics II . Bandung: Bandung Institute of Technology.
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  • Dhogal (1986). Basic Electrical Engineering Volume 1 . New York: Tata McGraw-Hill.
  • Gertshen, C., Kneser, HO, and Vogel, H. (1996). Physics: Magnetism Electricity and Optics . Jakarta: Center for Development and Language Development.
  • Ponto, Hantje (2018). Basic Electrical Engineering . Sleman: Deepublish.
  • Soebyakto (2017). Applied Physics 2 . Tegal: Publishing Agency of Pancasakti University of Tegal.
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