Conductors and insulators SA - CCEA

• Conductors have free electrons and insulators do not.

• Electric current in a metal is a flow of (free) electrons and the electrons move in the opposite direction to that of a conventional current.

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.

• 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

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.

The atoms in a metal are held together by strong bonds.

The atoms are close together and in a regular arrangement.

Metal atoms have loose electrons in the outer shells that can move from atom to atom.

These loose electrons are called free electrons.

They can move freely throughout the metal.

An electric current in a metal is the flow of these free electrons in one direction.

Energy is required to make the free electrons travel in one direction.

An electric cell, or a battery, can supply this energy and make free electrons move in a metal conductor connected between its two terminals.

Electrons flow from the negative terminal of the battery, through the conductor to the positive terminal.

They are repelled by the negative terminal and attracted by the positive terminal.

Electric current was discovered before physicists knew about free electrons.

It was originally thought that the current was flowing in the opposite direction, ie from the positive terminal of the battery, through the conductor, to the negative terminal.

For a number of reasons, although this is now known to be the wrong direction, it is still the direction of current marked on all circuit diagrams.

It is called the direction of conventional current.

Key points (Higher tier only)

• An electric current in a metal is a flow of free electrons in one direction.

• The direction of conventional current is from the positive terminal of a battery, through the conductor, to the negative terminal.

• The direction of free electron flow is from the negative terminal, through the conductor, to the positive terminal.

• The direction of conventional current is the direction marked on all circuit diagrams.

• The symbol for electric current is I.

Every cell and battery has a positive (+) terminal and a negative (-) terminal.

The longer line is the positive (+) terminal.

The shorter line is the negative (-) terminal.

So, in the case of a cell:

In circuit diagrams the positive side of a cell or battery is represented by the longer line and the negative side is represented by the shorter side.

This is referred to as the polarity of the cell.