Electric switch is a device that turns on or off the flow of electric current in a circuit. Light switches are common electric switches. In such switches, an insulated handle activates a hidden mechanism that completes or breaks the circuit. Turning the switch on connects two metal contacts so that current flows through the circuit. Turning it off separates the contacts and breaks the flow of current. Other electric switches operate without human control. For example, a thermostat switches on or off based on temperature. Computer chips contain many tiny switches called transistors (see Transistor ).
Electric switches may be classified according to the arrangement of their contacts. The simplest kind, a single pole, single throw switch, controls the flow of current along a single path. A double pole, single throw switch has two sets of contacts controlled by the same handle. In this way, two circuits can be controlled at the same time. A pair of single pole, double throw switches allows a light to be turned on and off from either of two locations. Each switch moves a contact back and forth between two wires. Electric current flows when the contacts in both switches are connected to the same wire. Flipping either of the two switches breaks the circuit by moving one contact to the other wire.
