Circuit

A circuit is another word for circle or loop. In computers, a circuit is continuous path along which electricity flows.

Since most computer technology uses electricity and electricity won't function unless the circuit is open, the concept of a circuit is important. For most discussions, the term circuit simply refers to an electrical loop. You see, electricity is a funny animal. It won't flow outwards unless there is a return path back to the source. This means that electricity really does flow in a circle, or 'circuit'. This concept is also used to describe other things like radio communication and fiber optics as well because they too are energy and behave much as electricity does.

There are several terms used in describing the behavior, conditon or state of a circuit.

OPEN, Closed and SHORT CIRCUITS

Open Circuit

An OPEN circuit is an incomplete electrical pathway. A cut in the wire, a blown fuse, anything that increases resistance to electricity somewhere in the path creates an open circuit. Note that cutting or disconnecting a portion of an electrical circuit creates an 'air gap' between the wiring or conductors. This air gap increases the electrical resistance of the circuit and breaks the electrical connection.

Closed Circuit

A closed circuit is a path which could allow electricity to flow across the circuit from an area of strong charge to an area of weak charge. It is important to remember that a closed circuit might not actually have an electrical current applied to it, but still be a closed circuit.

Short Circuit

A SHORT is when the electricity doesn't flow along the expected path. This could be because the connection is cross-connecting somewhere else, or grounding to another source of electricity. Simply put, the circuit is completing before it gets to where we actually want the electricity to flow to. This is why we talk about burnt wiring having shorted out.

Here's a simple trick to remembering the difference between the terms. Think about the classic science experiment with a battery, a light bulb, some wire and one of those funny-looking switches with the long lever and big contacts. The wires connected the battery to the switch and the bulb. When the switch lever was lifted, the circuit is open. When the switch lever is down, the circuit is closed and the lightbulb lights up. Note that if you leave the switch lever down until the battery goes completely dead, the electrical circuit is still considered a closed circuit.

If our little closed circuit is crossed with a separate piece of wire that completes the circuit before it gets to the bulb, it causes the electricity to run across a shorter path, and is called a short circuit.