Electric Current

Electric Current

Current tells us how quickly electric charge is moving through a circuit.

If more charge passes each second, the current is larger.

**I = Qt**

Electric Current

Electric current is the rate at which electric charge passes through a point in a circuit.

The equation is:

**I = Qt**

where:

I = current in amperes (A) Q = charge in coulombs (C) t = time in seconds (s)

One ampere means one coulomb of charge passing a point each second:

**1 A = 1 C/s**

Charge Carriers

In metallic wires, the mobile charge carriers are electrons.

When a potential difference is applied across a conductor, free electrons gain an overall drift through the material.

Conventional Current

By convention, current direction is taken from the positive terminal toward the negative terminal in the external circuit.

Electron drift is in the opposite direction.

Current in a Closed Circuit

A continuous current requires a complete conducting path and a source that maintains a potential difference.

If the circuit is broken, continuous current stops.

Worked Example

A charge of 24 C passes through a wire in 6 s.

**I = Qt**

**I = 246**

**I = 4 A**

Electric Current — Advanced

Current is a rate quantity. In a metallic conductor, electrons already exist throughout the wire; applying an electric field produces a small average drift velocity superimposed on their random motion.

The electrical effect is established through the circuit much faster than individual electrons drift from one end to the other.