Which statement correctly describes direct current compared to alternating current?

• A. Direct current maintains a constant polarity, while alternating current reverses polarity
• B. Direct current reverses polarity, alternating remains constant
• C. Both have the same polarity over time
• D. Direct current has higher frequency

Answer: (A)

The main idea is how current direction and polarity behave in direct current versus alternating current. Direct current flows in one unchanging direction, so its polarity stays fixed—the same electrode remains the positive or negative side throughout use. Alternating current, on the other hand, reverses direction periodically, so the polarity at the electrodes flips with each cycle. Because of that reversal, the polarity isn’t constant over time. In terms of frequency, direct current has essentially zero repetition of polarity (no cycle of reversal), while alternating current is defined by its frequency—the number of times per second the current reverses direction. This is why the statement that correctly describes the difference is that direct current maintains constant polarity, while alternating current reverses polarity.