School for Champions

Alternating Current (AC) Electricity

by Ron Kurtus (revised 11 September 2005)

Alternating current or AC electricity is the type of electricity commonly used in homes and businesses throughout the world. While the flow of electrons through a wire in direct current (DC) electricity is continuous in one direction, the current in AC electricity alternates in direction. The back-and-forth motion occurs between 50 and 60 times per second, depending on the electrical system of the country. AC is created by an AC electric generator, which determines the frequency. What is special about AC electricity is that the voltage in can be readily changed, thus making it more suitable for long-distance transmission than DC electricity. But also, AC can employ capacitors and inductors in electronic circuitry, allowing for a wide range of applications.


Electrons have negative (-) electrical charges. Since opposite charges attract, they will move toward an area consisting of positive (+) charges. This movement is made easier in an electrical conductor, such as a metal wire.

With DC electricity, connecting a wire from the negative (-) terminal of a battery to the positive (+) will cause the negative charged electrons to rush through the wire to the positive charged side. The same thing happens with a DC generator, where the motion of coiled wire through a magnetic field pushes electrons out of one terminal and attracts electrons to the other terminal.

With an AC generator, a slightly different configuration alternates the push and pull of each generator terminal. Thus the electricity in the wire moves in one direction for a while and then reverses its direction when the generator armature is in a different position.

Note: Although DC electricity can be created by a DC generator or a chemical battery, AC electricity is only created with an AC generator.

Motion of electrons

This illustration gives an idea of how the electrons move through a wire in AC electricity. Of course, both ends of the wire extend to the AC generator or source of power.

electrons in motion

The charge at the ends of the wire alternates between negative (-) and positive (+). If the charge is negative (-), that pushes the negatively charged electrons away from that terminal. If the charge is positive (+), the electrons are attracted in that direction.

Rate of change

AC electricity alternates back-and-forth in direction 50 or 60 times per second, according to the electrical system in the country. The frequency is designated as either 50 Hertz (50Hz) or 60 Hertz (60Hz).

Many electrical devices--like light bulbs--only require that the electrons move. They don't care if the electrons flow through the wire or simply move back-and-forth. Thus a light bulb can be used with either AC or DC electricity.


The major advantage that AC electricity has over DC is that AC voltages can be transformed to higher or lower voltages. This means that the high voltages used to send electricity over great distances from the power station could be reduced to a safer voltage for use in the house.

Changing voltages is done by the use of a transformer. This device uses properties of AC electromagnets to change the voltages.


In conclusion

We commonly use AC electricity to power our television, lights and computers. In AC electricity, the current alternates in direction. AC electricity was proven to be better for supplying electricity than DC, primarily because the voltages can be transformed. AC also allows for other devices to be used, opening a wide range of applications.