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.

Energy is required to make the free electrons travel 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 = \frac{\text{quantity of charge Q}}{\text{time taken t}}

I = \frac{\text{Q}}{\text{t}}

Triangle showing the relationship between current I and quantity of charge Q

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 = \frac{\text{Q}}{\text{t}}I = Q ÷ t
Q = ItQ = I x t
t = \frac{\text{Q}}{\text{I}}t = Q ÷ I

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