Voltage and resistance
Voltage drives current through a circuit, and resistance opposes it — for many materials the three are linked by Ohm's law: voltage equals current times resistance.
Practise this conceptVoltage is the energy given to (or taken from) each unit of charge as it moves between two points — not something that flows through a wire the way current does, but more like a difference in "electrical height" that drives the flow. It makes sense to talk about the voltage across a component, but not really the voltage "in" a wire the way you'd talk about current in it.
Resistance is whatever opposes that flow, converting some of the electrical energy into heat as charge pushes through. For many materials over a reasonable range of conditions, voltage, current and resistance lock together neatly through Ohm's law: voltage equals current times resistance.
Not everything obeys Ohm's law with a fixed resistance, though. A light bulb's filament resistance climbs noticeably as it heats up, and diodes barely conduct at all below a threshold voltage before conducting easily above it — Ohm's law describes a useful, common special case, not a universal rule that every material has to follow.
Key ideas
Requires: Electric charge and current
Unlocks: Capacitance
Formulas
| Symbol | Name | Unit |
|---|---|---|
| voltage | V (volt) | |
| electric current | A (ampere) | |
| resistance | ohm (ohm) |
Common misconceptions
- Voltage is a quantity that flows through a circuit, like current.
- Increasing the resistance in a circuit increases the current, for a fixed voltage.
- All materials obey Ohm's law exactly, with a constant resistance regardless of conditions.