# Charge and current

An electric current is a flow of charged particles.

In metal conductors the charged particles are free electrons.

The electrons are free to move from one ion to another and a net flow of these electrons in one direction is an electric current.

A source of energy, such as a cell or battery, is required to make the free electrons move in one direction.

## Charge

Electrons are negatively charged particles and they transfer electrical energy from a cell, through conducting wires, as an electric current.

Charge is measured in coulombs, C.

The charge of an electron is 1.6 x 10-19 C.

In other words, it takes 6,250,000,000,000,000,000 electrons to make up 1 coulomb of charge.

A coulomb of charge is just a very large group of electrons.

The relationship between current I and quantity of charge Q

An electric current is a flow of charged particles.

The size of an electric current is the rate of flow of charge.

Current I =

I =

This is often remembered as:

Quantity of charge Q = current I x time t

Q = It

Where:

Q = quantity of charge in coulombs, C

I = current in amperes, A

t = time in seconds, s

 I = I = Q ÷ t Q = It Q = I x t t = t = Q ÷ I

One ampere is the current that flows when one coulomb of charge passes a point in a circuit in one second.