Video Transcript
Which of the following sentences
correctly describes alternating current? (A) Alternating current is a
current that never reverses direction. (B) Alternating current is a
current that periodically reverses direction. (C) Alternating current is a
current that can sometimes reverse direction. (D) Alternating current has a
constant magnitude and always has the same direction.
The first thing we can say about
alternating current is that the name comes from the fact that it does indeed change
direction. Considering a closed loop of wire,
if alternating current existed in this wire, sometimes the charge would flow in this
direction, and sometimes it would flow the opposite way. That’s what it means for current to
change direction.
Reviewing our four answer options,
option (A) says that alternating current never reverses direction and option (D)
says that alternating current always has the same direction, in other words that it
doesn’t reverse direction. Neither of these answer options is
correct. Alternating current does change
direction; that’s how it gets its name.
Both of our remaining choices
describe current that either does change direction or current that can. Not only does alternating current
change direction, but it does so at even intervals of time. This means that if alternating
current, say, spends five seconds traveling in a clockwise direction, then it will
spend the next five seconds traveling in a counterclockwise direction and then five
more seconds in a clockwise direction then five more in a counterclockwise. It goes back and forth like this,
and it does so periodically. This is another way of saying the
current changes direction at even intervals of time. For our answer, we choose option
(B). Alternating current is a current
that periodically reverses direction.
