What Is an Electric Circuit?

An electric circuit is a complete, unbroken path along which electricity can travel out of an energy source, through the parts of the circuit, and back into the source again.

A working circuit needs three things:

1. An energy source — usually a cell (what people call a "battery"). Two or more cells joined together are properly called a battery.
2. A conducting path — connecting wires, joined at both ends of the cell.
3. Something that uses the energy — a bulb, a buzzer or a small motor.

If the path is complete, the bulb lights. If there is any gap — a loose wire, a flat cell, a broken bulb — nothing works, no matter how good the other parts are.

Worked example — the torch that will not light.

A learner builds a circuit with one cell, two wires and a bulb, and it stays dark. She checks it in order:

• Is one wire connected to each end of the cell? (Both ends must be used — one wire alone can never make a circuit.)
• Are both wires firmly touching the metal of the bulb holder?
• Is the bulb's thin wire inside the glass unbroken?
• Is the cell fresh?

She finds a loose crocodile clip, presses it home, and the bulb lights. There was never anything wrong with the electricity — only with the path.