Glossary
transformer
A transformer is two coils sharing a core; it changes alternating voltage by the ratio of turns between them — more turns on the secondary steps the voltage up, fewer steps it down.
A transformer is two coils sharing a core, and it moves energy between them through the magnetic field in that core. It changes alternating voltage, and it cannot work on direct current, because a steady current creates no changing field for the second coil to pick up.
The rule is the turns ratio. Divide the turns on the secondary by the turns on the primary and you have the factor by which voltage changes: 1,000 turns on the secondary against 100 on the primary multiplies the voltage by ten. More turns on the secondary makes a step-up transformer, fewer makes a step-down one. Voltage and current trade off, so whatever a transformer adds in volts it gives back in current, and the power either side stays the same.
That trade is why the grid uses them: voltage is stepped up for transmission so less energy is lost as heat in the wires, then stepped down close to the homes that use it.
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)