Grade 12 · Physics
Circuits
Why it matters
Current, voltage, resistance.
Advanced20m readingPrerequisite: Electric fields
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.
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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.