What goes from + to - and then - to +?

What goes from + to - and then - to +?

• A. AC (alternating current)
• B. DC (direct current)
• C. Pulsating DC
• D. Capacitive current

Answer: (A)

Alternating current is defined by its polarity reversing regularly, going from positive to negative and back again. This happens in a periodic waveform (usually a sine wave) so the direction of current flow continually switches. In power systems, this reversal occurs at the system frequency (for example, 60 times per second per cycle in many places, which means the direction switches 120 times per second). Direct current, by contrast, flows in one direction only, even if its magnitude changes. Pulsating DC can vary in magnitude and may briefly reach zero, but the current doesn’t reverse direction—the overall flow remains in the same orientation. Capacitive current describes charging and discharging through a capacitor in response to changing voltage, which can involve lead/lag behavior but isn’t defined by a complete reversal of current direction each cycle. So the scenario described—polarity switching from + to - and back—fits alternating current.

Alternating current is defined by its polarity reversing regularly, going from positive to negative and back again. This happens in a periodic waveform (usually a sine wave) so the direction of current flow continually switches. In power systems, this reversal occurs at the system frequency (for example, 60 times per second per cycle in many places, which means the direction switches 120 times per second).

Direct current, by contrast, flows in one direction only, even if its magnitude changes. Pulsating DC can vary in magnitude and may briefly reach zero, but the current doesn’t reverse direction—the overall flow remains in the same orientation. Capacitive current describes charging and discharging through a capacitor in response to changing voltage, which can involve lead/lag behavior but isn’t defined by a complete reversal of current direction each cycle.

So the scenario described—polarity switching from + to - and back—fits alternating current.