Relay
Appearance
![](http://178.128.105.246/host-http-upload.wikimedia.org/wikipedia/commons/thumb/8/8a/Electronic_component_relays.jpg/220px-Electronic_component_relays.jpg)
A relay is an electromagnetically operated switch. It was invented in the 19th century to make electric telegraph signals go farther. Nowadays relays control circuits with low-voltages. Many machines use them, including vehicles and electronics.
![](http://178.128.105.246/host-http-upload.wikimedia.org/wikipedia/commons/thumb/4/4a/Commons-logo.svg/30px-Commons-logo.svg.png)
Wikimedia Commons has media related to Relays.