AC/DC
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 URL:
http://www.youtube.com/watch?v=JZjMuIHoBeg
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 battery-powered 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.
Summary
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Direct current (DC) keeps flowing in just one direction. Batteries provide direct current.
Alternating current (AC) keeps reversing direction. Power plants provide alternating
current.
Vocabulary
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alternating current (AC): Electric current that keeps reversing the direction in which the
current flows.
direct current (DC): Electric current that flows only in one direction.
Practice
At the following URL, watch the video comparing direct and alternating current. Then answer
the questions below. http://www.diffen.com/difference/Alternating_Current_vs_Direct_Current
1.
2.
3.
4.
5.
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?
Review
1. Compare and contrast direct and alternating current