RelaysRelays are basically switches that are controlled by electricity rather than mechanical input. Inside the relay, the current used to alter the state of the switch is put into a coil. As we now from previous pages, the coil generates a magnetic field. That electric field acts upon a spring loaded metal contact. When there is no current flowing the spring loaded contact is pulled up against the first output contact completing the input to first output circuit. When current is passed through the coil, a magnetic field is generated and the input contact is pulled down, against the force of the spring, to the second output contact. So whether the coils has current in it or not controls whether the circuit should be completed to output one or two.
Relays are represented by this symbol: