Glossary
direct current
Direct current (DC) is current that flows in one direction only, at a steady value. Batteries, solar panels and the electronics inside a device all run on it.
Direct current, or DC, flows in one direction only and holds a steady value. Batteries and torch cells give DC, solar panels produce it, and the output of a car's charging system is DC. Nearly every electronic circuit inside a device runs on it.
Its counterpart is alternating current, which reverses direction many times every second. The two are easiest to keep apart by their sources: batteries and electronics supply DC, while the power arriving at a wall socket is AC.
Three consequences are worth remembering. DC cannot be stepped up or down by a transformer, so the grid moves power as AC and converts to DC at the device. A diode and an LED conduct in one direction only, and that is how an adapter turns AC into DC. Finally, polarity matters: reversing the connections to a DC circuit reverses the current, so a device wired backwards may not run at all.
Taught in
Related terms
- alternating current — Alternating current (AC) reverses direction at a regular frequency — 60 cycles per second in North America — and is the current a wall outlet supplies.
Source: Official ASVAB — subtest descriptions (what each subtest asks) and the CAT-ASVAB scored-question counts (accessed 2026-09)