A relay is an electrically operated (required DC voltage to operate) switch that allows you to turn ON or OFF a circuit which has higher voltage or current than a micro-controller could handle.
Electromagnetic Relay: Relay work on the electromagnetic principle. The DC supply magnetizes the coil of the relay. The field attracts an iron armature, whose other end pushes the contacts together, completing the circuit.
For Example: If you need to turn OFF / ON your AC (Alternate Current ) lamp of 220 V by using a micro-controller ( operate at 5 V) can be done only by using a relay. The relay protects the DC circuit from the AC circuit.
Construction
Essential components of an Electromagnetic Relay:
Electromagnetic coil
Control Spring
Contact Point
Electromagnetic Coil: A iron rod covered by copper turn which becomes a magnet when we supply DC voltage to it.
Control Spring: It is used to control the spring when an electromagnetic coil attracts the contact point. It gains its original shape when an electromagnetic coil is demagnetized. A spring controls the movement of the rod.
Contact Point: When an electromagnetic coil is magnetized contact point closed. It provides a continuous path to the alternating current.
Working
When an electromagnetic coil is demagnetized.
In this condition, the DC supply to an electromagnetic is OFF. So, the coil is not magnetized. The contact point is in a normal position as attached with the spring. As you see in the figure, the phase line is disconnect due to which AC circuit is open.
When an electromagnetic coil is magnetize.
In this condition, the DC supply to an electromagnetic is ON. So, the coil is magnetized. The contact point changes its position. Spring starched slightly as the force of attraction is higher than the strength of restraining(Spring Force). Now, it provides a closed path of the AC circuit and bulb start glowing.
