Alternating Current

After reading this section you will be able to do the following:

  • Define what AC stands for and what it means.
  • Explain how AC is created and delivered to different places.
  • Discuss the differences between AC and DC.

AC is short for alternating current. This means that the direction of current flowing in a circuit is constantly being reversed back and forth. This is done with any type of AC current/voltage source.

The electrical current in your house is AC. This comes from power plants that are operated by the electric company and is carried through power lines.  The direction of current is switching back and forth 60 times each second (60 Hertz) in the United States. The unit Hertz (Hz), which is defined as the number of cycles per second, is used to describe the frequency at which the AC alternates.  

This is a circuit using an AC source of electricity. Notice that the light bulb still lights but the electron current is constantly reversing directions. The change in direction of the current flow happens so fast that the light bulb does not have a chance to stop glowing. The light bulb does not care if it is using DC or AC current. The circuit is delivering energy to the light bulb from the source, which, in this case, is a power plant.


  1. AC, or alternating current means the electrical current is alternating directions in a repetitive pattern.
  2. AC is created by generators in power plants, and other sources.
  3. This AC current is delivered to our homes and businesses by the power lines we see everywhere.