Why does a bulb only light up when the wires make a loop?

Picture a battery, two wires and a small bulb from a science kit, lying on the table. You touch the wire ends in place, and the bulb glows warm and yellow. Then one wire slips off, and the light goes out at once.

Why does the bulb only shine when the wires make a loop, from the battery to the bulb and back again? Let's follow the path and see.

Everything starts at the battery. A battery has two ends, and it pushes electricity out of one end into the first wire. That push is what sets the electricity moving.

The electricity travels along the metal inside the wire. Metal lets electricity pass through easily, so the wire works like a road that carries it to the bulb.

Inside the bulb, the electricity has to squeeze through one very thin wire. All that squeezing heats the thin wire until it glows, and that glow is the light you see.

From there, the electricity keeps going. It leaves the bulb, runs along the second wire, and comes back into the other end of the battery. The battery pushes it round again, over and over.

This whole round path has a name. We call it a circuit, which means a loop that electricity travels all the way around.

The electricity in a circuit moves all together, like the links of a bike chain going round. Each bit pushes the next bit along the loop. Now imagine a gap far away from the bulb, right next to the battery. Would the bulb still glow?

No, the bulb goes dark. Electricity cannot jump across the air in a gap, so a gap anywhere breaks the circuit. Just like a snapped bike chain, all the electricity stops moving at once, and the thin wire in the bulb stops glowing.

Let's remember one word: circuit. The battery can only push electricity through the thin wire in the bulb to make it glow when the electricity has a full circuit to travel round and come back to the battery.

Goodnight, bright explorer, and may your dreams glow as softly as that small bulb.