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The particles in a metal are held together by strong metallic bonds.

The particles are close together and in a regular arrangement.

Metals atoms have loose electrons in the outer shells, which form a 'sea' of delocalised or free negative charge around the close-packed positive ions.

These loose electrons are called free electrons.

They can move freely throughout the metallic structure.

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

Direction of flow of free electrons

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

An electric cell (often called 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 through the conductor to the positive terminal.

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

The direction of conventional current

Electric current was discovered before physicists knew about free electrons.

It was originally thought that the current was flowing in the opposite direction, i.e. 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

• The direction of conventional current is from the positive terminal, 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.