Electric Circuit

An electric circuit is a closed loop that lets electricity flow from one place to another. The loop has to be complete, like a racetrack with no gaps. If the loop is broken anywhere, the electricity stops. Circuits are what make flashlights glow, phones buzz, and refrigerators hum.

Every circuit needs three basic parts. First, a source of energy, like a battery or a wall outlet. Second, a path for the electricity to travel, usually wires made of copper. Third, something that uses the energy, called a load. A light bulb is a load. So is a motor, a speaker, or a heater.

Electricity in a wire is a flow of tiny particles called electrons. Electrons are parts of atoms, and they carry a small electric charge. When a battery is hooked up to a wire, it pushes electrons through the wire. This flow is called an electric current. Current is measured in units called amperes, or amps for short.

Most circuits also have a switch. A switch is just a gap in the loop that you can open or close. When you flip a light switch up, two metal pieces touch and the loop is complete. When you flip it down, the pieces pull apart and the loop breaks. The light turns off because the electrons have nowhere to go.

Circuits come in two main types. In a series circuit, everything is connected in one single line. If one bulb burns out, the whole line goes dark, because the loop is broken. Old Christmas lights worked this way, which is why one bad bulb used to ruin the whole string. In a parallel circuit, each part has its own branch back to the battery. If one bulb burns out, the others stay lit. The wiring in your house uses parallel circuits.

A wire alone can be dangerous. If electrons flow too fast through a thin wire, the wire heats up and can start a fire. To prevent this, circuits use safety parts called fuses or circuit breakers. When too much current flows, the fuse melts or the breaker flips, and the loop opens before anything catches fire.

The Italian scientist Alessandro Volta built the first real battery in 1800. Before that, people knew about sparks and shocks, but they could not store electricity or make it flow steadily. Once they could, the modern world began to wire itself together.