A characteristic of alternating current is that it:

• A. changes polarity 60x per second
• B. flows in one constant direction
• C. has fixed polarity
• D. remains at constant magnitude

Answer: (A)

Alternating current is defined by its polarity reversing periodically, unlike direct current which keeps the same direction. The frequency tells how many complete cycles occur each second; at 60 Hz, the wave repeats 60 times every second, so the polarity shifts with each half-cycle, effectively changing sign about 60 times per second. This also explains why the instantaneous magnitude is not constant, since it rises to a peak and falls to zero each half-cycle, even though the overall power level can be steady through the RMS value. The other statements don’t fit because AC does not flow in one constant direction, it does not have fixed polarity, and its instantaneous magnitude varies over time.