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All matter consists of atoms.

Atoms contain three types of smaller particles: protons, neutrons and electrons.

• Protons are positively charged;
• Electrons are negatively charged;
• Neutrons have no charge – they are neutral.

Protons and electrons are called charged particles.

Protons and neutrons are found inside the nucleus.

Electrons orbit the nucleus.

An atom is neutral because it contains the same number of protons and electrons.

Electric current

An electric current is a flow of charged particles in one direction.

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

Electric current is measured in amperes (A), or amps for short, using an ammeter.

The symbol used for electric current is I.

For example, I = 3 A, means a current of 3 amps.

A material that allows electricity to pass through it is called a conductor.

A material that does not allow current to pass through it is called an insulator.

In general materials made from metal are good conductors of electricity.

Materials made from non-metals are insulators, or poor conductors of electricity.

Key points

• An electric current is a flow of charged particles in one direction.
• Metals such as copper and silver are good conductors of electricity.
• Non-metals such as plastic and rubber are insulators or poor conductors of electricity.
• Electric current is measured in amps, A, with an ammeter.