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Glossary Science & Engineering

Ohm's law

Ohm's law states that the current through a conductor equals the voltage across it divided by its resistance: `V = I × R`.

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In more detail

12 volts across 4 ohms drives 3 amps, which dissipates P = V × I = 36 watts. Knowing any two of voltage, current, resistance and power lets you find the other two.

Try these tools

Ohm's Law Calculator

Solve for voltage, current, resistance, or power using Ohm's Law — enter any two known values and calculate the rest.

Electrical Power Calculator

Convert between watts, volts and amps for DC, single-phase and three-phase AC, with power factor, apparent and reactive power.

See also

  • Glossary Resistor
    A resistor is a component that limits current in a circuit, with a value in ohms often shown by coloured bands.
  • Glossary Kilowatt-hour (kWh)
    A kilowatt-hour is the energy used by a 1,000-watt device running for one hour, the unit on electricity bills.
  • Cheat sheet Electrical Formulas Cheat Sheet
    Ohm's law, power, series and parallel resistors, voltage dividers, LED resistors, cable voltage drop.
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