Electric Currents in Conductors

Charges experience force in an electric field. If these charges are free to move, their motion constitutes an electric current.

In ordinary matter, many electrons are bound to atoms. In metals, however, some electrons are free to move through the material, so metals behave as conductors.

A conductor allows charge to move easily because it contains mobile charge carriers, mainly free electrons in metals.

A conductor is a material in which some charges are free to move from one part of the material to another.

Key Concept

• In solid metallic conductors, the positive ions remain fixed in position.
• The current is carried by mobile electrons.
• In electrolytes, both positive and negative ions may move, but this note focuses on solid conductors.

Quick Comparison

Metals contain a large number of electrons that are not tightly bound to individual atoms. These electrons can move through the bulk of the conductor.

This is the main reason metals conduct electricity effectively.

Analogy

A useful analogy is to imagine students standing in fixed rows while a few balls are free to roll between them. The fixed students resemble metal ions, while the moving balls resemble free electrons.

Even when no electric field is applied, free electrons in a metal are not at rest. They move randomly due to thermal energy.

These electrons frequently collide with the fixed ions of the metal. Because their directions keep changing randomly, the average current in the conductor is zero.

When an external electric field is applied, each free electron experiences a force. As a result, the electrons acquire a slow net drift in one preferred direction, and an electric current is produced.

The source material describes a metallic cylinder placed between oppositely charged ends, showing that electrons drift toward the positively charged side.

• Random motion: Irregular motion of electrons due to thermal energy.
• Drift motion: Net-directed motion of electrons under an electric field.
• Electric current: Flow of charge through a conductor.

If the ends of a conductor are merely given charges such as +Q and -Q, current flows only for a short time. This happens because the charges at the ends are gradually neutralised.

A steady current is obtained only when a source, such as a cell or battery, continuously maintains the potential difference and electric field inside the conductor.

A battery is needed:

• It replenishes charges at the ends of the conductor.
• It maintains a steady electric field in the conductor.
• It allows current to continue for a long time instead of stopping quickly.