Grade 11 · Physics
Circuits
Why it matters
Current, voltage, resistance.
Last reviewed 2026-09-03 · accuracy standard
What is Ohm’s law?
Short answer
Ohm’s law states that the current through a conductor is directly proportional to the voltage across it and inversely proportional to its resistance: V = IR. Voltage is measured in volts, current in amperes, and resistance in ohms. It lets you find any one of the three quantities in a simple circuit when the other two are known.
Concept preview
What you will be able to do
- 01Define current, voltage and resistance and their units
- 02Apply Ohm's law
- 03Analyse series and parallel resistor combinations
An electric current is simply flowing charge. Its size is the amount of charge passing a point each second: , measured in amperes (A), where one amp is one coulomb per second. By a historical convention, conventional current flows in the direction a positive charge would move — from to outside the battery — even though in a metal wire it is actually the electrons drifting the other way. A current needs a complete, unbroken loop: break the circuit and the flow stops instantly.
School Plan
Circuits
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Related topics
Frequently asked questions
- What are the units in Ohm’s law?
- Voltage in volts (V), current in amperes (A), and resistance in ohms (Ω).
- Do all materials obey Ohm’s law?
- No. Ohmic materials have constant resistance; non-ohmic components like diodes and filament bulbs do not follow V = IR linearly.