The switch is a device used to control the flow of electrical current into the circuit. In the previous discussion about electric current, the electrical current will only flow in a closed circuit. So as to create a current to flow or not, we can use the switch.
Current flows when the switch contacts touch each other. In this state, the switch is said to be closed or made contact.
Current can not flow into the circuit when the contacts are not touching. In this state the switch is said to be opened or lost contact.
Other terms of the condition of the switch is On and Off. On condition occurs when the contacts is made, and the Off condition occurs when the contact is lost.
There are various types of switches are used for many different purposes. Figure above shows the general symbols of switch, Off the conditions shown in Figure A, and On conditions are shown in Figure B.