Voltage, current, and resistance
CERT 1 · DC/AC Theory & Safety · ~10 min
Think of a circuit as a closed water loop. Voltage (V) is the pump pressure — the electrical potential difference that pushes charge. Current (I) is the flow rate, measured in amperes: one ampere is one coulomb of charge passing a point per second. Resistance (R) is the pipe's narrowness — opposition to flow, measured in ohms (Ω).
These three are locked together: raise the pressure and flow increases; narrow the pipe and flow decreases. That relationship is Ohm's Law, the single most-used equation in the trade, and the subject of Unit 1.3.
Materials matter. Copper is the trade's default conductor because of its low resistivity and workability. Insulators — the colored thermoplastic around each conductor — have resistivity so high that, intact, effectively no current crosses them.
Exam focus: expect definition questions phrased as units ('one coulomb per second is…') and analogy questions. Know the unit, symbol, and role of each quantity.
Quiz — 3 questions
1. In the water analogy, current corresponds to:
2. One ampere equals:
3. Copper is the default trade conductor mainly because of its: