According to a certain task, the required devices, connected by wires that is composed of circuits. Circuits are the main components of electric power systems, control systems, communication systems, computer hardware and other electrical systems, play a role in the generation, transmission, conversion, control, processing and storage of electrical energy and electrical signals.
The simplest circuit is made up of components such as a power supply, electrical appliances (loads), wires, and switches. When a circuit is on, it is called an open circuit, and when it is off, it is called an open circuit. Only when a circuit is open can current pass through it. A break in the circuit is called a break or an open circuit. If there is no load between the positive and negative terminals of the power supply in the circuit, it is called a short circuit, which is never allowed. Another kind of short-circuit is that the two ends of a component are directly connected, and then the current flows from the direct connection without passing through the component, which is called a short-circuit of the component. Open circuit (or broken) is allowed, and the first short circuit is never allowed, because the short circuit of the power supply will lead to the power supply burned out, the short circuit of the electrical appliances will lead to electrical appliances, meters, etc., can not work properly phenomenon occurs.