voolutugevus

Voolutugevus, in Estonian also meaning electric current strength, is the rate at which electric charges flow through a conductor. It is a fundamental quantity in electricity and is represented by the symbol I. When defined at a given moment, it is the instantaneous current, measured in amperes (A).

The SI unit is the ampere. An ampere corresponds to a flow of one coulomb of charge per second. In practical circuits, current is often described by its root-mean-square (rms) value for alternating current, which equals the effective DC equivalent that delivers the same power. The average current over a complete cycle may be zero for AC waveforms with symmetrical duty cycles. Current is measured with an ammeter, placed in series with the circuit element under test; in many cases a clamp meter around a conductor is used for non-contact measurement.

Ohm's law gives I = V/R for a resistor, showing current depends on voltage and resistance. In series circuits, the current is the same through all components, while in parallel circuits it divides among branches in inverse proportion to each branch's resistance. Kirchhoff's current law states that the sum of currents entering a junction equals the sum leaving.

Real-world currents range widely: a small LED may draw tens of milliamperes; household devices vary from fractions of an amp to several amperes; mains voltages of 110–240 V produce larger currents in resistive loads. Excessive current can cause overheating and damage; protective devices such as fuses and circuit breakers limit current.

See also Ohm's law, ammeter, resistance, electrical safety.