In this topic you will learn how to control the flow of electricity.

Light bulbs can be connected in a series circuit. A series circuit is a circuit in which the current must flow through one bulb in order to flow through another. When both bulbs are in place in a series circuit, they form a closed circuit. When one bulb is removed, an open circuit is created. In an open circuit, current cannot complete its path. The remaining bulb does not light. A series circuit is a type of system that does not work when a part is removed.

Two bulbs can also be connected in a parallel circuit. A parallel circuit is a circuit in which each bulb is connected to the electric current separately. When you remove one bulb from a parallel circuit, the other bulb is still part of a complete circuit. A parallel circuit is a type of system that still works when a part is removed because there is still a complete circuit.

A short circuit is dangerous. Too much current flows in a short circuit. This can cause wires to heat up. Hot wires can start a fire. Too much current can also damage electric devices. One device that keeps too much electric current from flowing through wires is a fuse. A fuse has a thin strip of metal in it. The fuse is a resistor. When current flows through the resistor, it heats up. If a dangerously high current flows through the fuse, the metal strip melts. This creates an open circuit. The current stops flowing. Once a fuse melts, it must be replaced with a new fuse.

In homes and other places, electric devices are connected in parallel circuits. If they were series circuits, then all the lights would go out if one bulb burnt out. These circuits are usually controlled by switches.

Most new homes do not have fuses. They are built with circuit breakers. A circuit breaker is a switch that protects circuits from dangerously high currents. When a dangerously high current flows through the switch, the metal becomes heated and expands. This pushes the switch open. A spring holds the switch open, creating an open circuit.

Understanding how electricity travels through parallel and series circuits gives you control over where it goes and what it does.