What makes a light bulb glow — and why does flipping one switch sometimes kill every light? Today you'll learn how circuits work, then you will predict which bulbs stay lit.
Before we start — every light switch you flip today uses this idea — what do you think is happening inside the wires?
A battery pushes electric current around a loop of wire and through a bulb, then back. If the loop is complete, the bulb lights. If there's any gap, the current stops and the bulb stays dark.
In a series circuit, everything sits on one loop, like beads on a string. The same current flows through every part in turn — so if you break the loop anywhere, everything goes out.
In a parallel circuit, each bulb sits on its own branch back to the battery. Each has a complete loop of its own — so removing one bulb doesn't affect the others. This is how the lights in your house are wired.