Question Video: Describing Alternating Current Science

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.

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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.

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