How does a switch turn a light on and off?

Click! You reach for the switch by the door, and the whole room fills with light. Click again, and the room goes dark. Next time, rest your finger on a switch and feel it tip up and down.

That little switch sits far away from the lamp up on the ceiling. So how does a switch turn a light on and off? Let's find out together.

A lamp needs electricity to shine. Electricity travels to the lamp along thin metal wires hidden inside your walls and ceiling. Metal lets electricity move through it easily, so the wires carry it like a road.

Electricity only flows when its path makes a full loop, from the wall out to the lamp and all the way back. This loop is called a circuit, which means a path that goes all the way round with no gaps. When a circuit has even one gap, the electricity stops moving.

As electricity flows around the loop, it passes right through the bulb. The bulb turns that moving electricity into bright light, and that glow is what you see.

The switch sits in the circuit, right on the path between the wall and the lamp. Inside it hide two small pieces of metal. When you press the switch on, one piece moves and presses against the other, so the path has no gap and the bulb lights up. Now, what do you think happens inside when you press the switch off?

You press it off, and the two metal pieces pull apart. A tiny gap of air opens between them, and electricity cannot cross air. The circuit is broken, so the electricity stops flowing and the bulb goes dark.

When you press a switch on, its two metal pieces touch, so electricity flows all the way round the circuit and the bulb shines. When you press it off, the pieces pull apart and leave a gap in the circuit, so the light goes out.

Up on the ceiling, the bulb glows warm and bright. Far below, inside the switch by the door, two tiny pieces of metal rest snugly together, holding the whole loop closed.