Like as light switch in your home Relay is just an electrically activated switch but with several important differences. Relay is electromagnetic switch. Relay function is to allow a low power control voltage to operate a high power switch.
Below are the examples of some switch that can be used in relays.
Note: Relays are same just as normal switch. As we control normal switch in our home manually, with the help of relay we can control switching with an electrical signal.
You stepped into a room in college and you flipped on the lights. It is a large room with many banks of overhead lights, but just one ordinary switch near the door. When you push the switch, you would hear a solid “thunk” sound somewhere overhead, and then a moment later the lights would begin to come on.
What was happening was that so many lights in such a large room drew so much current, that an ordinary switch could never handle it at all and so you could
- a) Use a lot of switches and divide up the load,
- b) Use one really big industrial switch that would be difficult, expensive, and unwieldy (difficult to move), or
- c) Use an ordinary light switch, to control a relay (at coil side) that could easily handle such a load. When you flipped the switch the “thunk” you heard was the sound of the relay throwing somewhere above the ceiling.
If lights in the lab are 220 volt lights, you can still switch them with 120 volts or even 12 volts.
Depending on the specifications of the relay that means you could use a relatively low voltage, low amperage output from a computer to control a large bank of lights, or a large motor, or most anything else.
As you learn function of relay now read next Working principle of relay