Simple circuits, conductors and insulators

A circuit must be complete

Electricity only flows round a closed loop: from one end of the cell, through the wires and the lamp, back to the other end. One gap anywhere — a broken wire, an open switch, a loose crocodile clip — and nothing works at all.

Conductors and insulators

A conductor lets electricity through: copper, iron, steel, aluminium. An insulator does not: plastic, rubber, wood, glass, dry cloth. That is why wires are copper inside and plastic outside.

Changing the circuit

Adding a second cell makes the lamp brighter. Adding a second lamp in the same loop makes both dimmer, because they share.