Concepts

Quantities & Units

Voltage, current, resistance and the SI units used to measure them.

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Voltage is the electrical pressure that drives current. Learn what a volt means, how EMF differs from terminal voltage, and how...

Electric current is the rate at which charge flows through a conductor. Learn the ampere, conventional current direction, curren...

Resistance opposes the flow of current and converts electrical energy into heat. Learn the ohm, resistivity, temperature effects...

Volts, amperes, ohms, watts and their prefixes form the language of electricity. Learn the SI units, derived units and how to co...

Every formula used here, with variable definitions, units, application conditions and a worked example.

Check your understanding with transparent calculators that show the formula and substitution.