Current flowing through a ____ circuit only changes when it is switched on or off; however, current flowing through a ____ circuit is constantly changing direction.

• A. DC; AC
• B. Series; Parallel
• C. Direct; Alternating
• D. AC; DC

Answer: (A)

Direct current keeps a single direction. Once a DC circuit is closed, the current flows steadily in one direction and only changes when you switch power on or off (or if the circuit conditions change in other ways). Alternating current, by contrast, continuously reverses direction because the source itself is changing polarity, producing a waveform that crosses zero and flips direction each half-cycle. In practical terms, a battery or DC power supply provides current that does not regularly reverse direction, while a typical wall outlet or generator provides AC whose current direction changes periodically. This is why the first blank describes DC behavior and the second describes AC behavior.