Direct and Alternating Current

Direct and Alternating Current
Jean Brainard, Ph.D.
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Printed: December 10, 2015
Jean Brainard, Ph.D.
Chapter 1. Direct and Alternating Current
Direct and Alternating
• Distinguish between direct current and alternating current.
To use an electric appliance, you have to plug it into an outlet unless it has batteries. This may be all you need to
know in order to use electric current. But did you ever wonder what electric current is or how it flows through wires
inside the walls of your home? Electric current is a continuous flow of electric charges. The charges may flow in
just one direction, or they may keep reversing direction. You can watch an animation of both types of current at this
Click image to the left or use the URL below.
Direct Current
When current flows in just one direction, it is called direct current (DC). The diagram below shows how direct
current flows through a simple circuit. An example of direct current is the current that flows through a batterypowered flashlight. In addition to batteries, solar cells and fuel cells can also provide direct current.
Alternating Current
When current keeps reversing direction, it is called alternating current (AC). You can see how it works in the two
diagrams below. The current that comes from a power plant and supplies electricity to homes and businesses is
alternating current. The current changes direction 60 times per second. It happens so quickly that the light bulb
doesn’t have a chance to stop glowing when the reversals occur.
Q: Which type of current flows through the wires in your home?
A: Alternating current from a power plant flows through the wires in a home.
• Direct current (DC) keeps flowing in just one direction. Batteries provide direct current.
Chapter 1. Direct and Alternating Current
• Alternating current (AC) keeps reversing direction. Power plants provide alternating current.
Explore More
At the following URL, watch the video comparing direct and alternating current. Then answer the questions below.
Current from a battery is __________ current.
Current from a power plant is __________ current.
In the U.S., alternating current reverses direction at a rate of __________ hertz.
What is the advantage of producing and using alternating current?
How can a device, such as a computer, that needs direct current use alternating current from a wall outlet?
1. Compare and contrast direct and alternating current.