What is the primary difference between AC and DC current?

What is the primary difference between AC and DC current?

• A. AC reverses direction periodically; DC flows in one direction with constant polarity.
• B. AC and DC are the same.
• C. DC reverses direction periodically; AC flows in one direction with constant polarity.
• D. AC decays quickly.

Answer: (A)

The key idea is how current behaves over time: alternating current reverses direction periodically, while direct current flows in one direction with constant polarity. This means AC’s flow and its voltage swing back and forth, whereas DC maintains a single direction and a steady polarity at a given point in the circuit. That fundamental difference explains why AC is used for power transmission—easy to transform voltages up and down—and DC is common in batteries and many electronic devices that require a steady, unchanging supply. (In practice, DC can have small ripples, and AC can be non-sinusoidal, but the defining trait is the reversal of direction for AC versus the single-direction flow for DC.)

The key idea is how current behaves over time: alternating current reverses direction periodically, while direct current flows in one direction with constant polarity. This means AC’s flow and its voltage swing back and forth, whereas DC maintains a single direction and a steady polarity at a given point in the circuit. That fundamental difference explains why AC is used for power transmission—easy to transform voltages up and down—and DC is common in batteries and many electronic devices that require a steady, unchanging supply. (In practice, DC can have small ripples, and AC can be non-sinusoidal, but the defining trait is the reversal of direction for AC versus the single-direction flow for DC.)