Which waveform reverses direction sinusoidally?

• A. Direct current (DC) reverses direction sinusoidally.
• B. Alternating current (AC) reverses direction sinusoidally.
• C. Pulsed current delivers current in bursts with off-times.
• D. Mixed waveform alternates amplitude with zero crossing.

Answer: (B)

Reversing direction sinusoidally means the current direction changes smoothly over time in a wave that follows a sine curve. This is a hallmark of alternating current, which periodically reverses direction. In a sinusoidal AC waveform, the current rises to a positive peak, crosses zero, reaches a negative peak, and returns to zero, repeating each cycle. Direct current stays in one direction and does not undergo this kind of smooth reversal. Pulsed current comes in bursts with off-times, so the direction isn’t reversing in a continuous sine fashion within a single waveform. A mixed waveform with amplitude changes and zero crossings may cross zero, but its reversal isn’t inherently a pure sine reversal. Therefore, the waveform that reverses direction sinusoidally is alternating current.