Which statement best describes AC voltage?

• A. A.C. voltage remains constant at a fixed value
• B. A.C. voltage is one that continually changes in magnitude and periodically reverses in polarity
• C. A.C. voltage flows only in one direction
• D. A.C. voltage is zero except at peak values

Answer: (B)

AC voltage is defined by its alternating nature: the instantaneous value changes with time and the polarity reverses every half-cycle. This means the waveform rises to a positive peak, crosses zero, then falls to a negative peak and back again. It is not constant and it does not push current in a single direction. It also isn’t zero except at peaks—the voltage crosses zero many times each cycle and reaches positive and negative peaks. So the statement that AC voltage continually changes in magnitude and periodically reverses in polarity best captures what AC voltage is.