What is the difference between DC and AC voltages?

• A. DC alternates; AC is constant.
• B. DC is constant; AC alternates in polarity and magnitude.
• C. DC is higher voltage; AC is lower voltage.
• D. DC is only used in batteries; AC only in outlets.

Answer: (B)

How voltages behave over time is being examined. Direct current keeps a constant potential difference in one direction, so the voltage is steady. Alternating current, on the other hand, continually changes its polarity and its magnitude, so the voltage rises and falls and the current reverses direction repeatedly. This distinction explains why DC comes from sources like batteries and fixed power supplies, while AC is delivered by wall outlets and the power grid. In practice, AC is described by its RMS value and frequency, which quantify its heating effect and how often it alternates each second. The statement that DC is constant and AC alternates in polarity and magnitude captures how the two types of voltages behave.