Electromagnetic Relay

Electromagnetic relay, also known as relay, is one of the most important devices in use today in various applications. For instance, when you turn the car engine on, you use a relay, an electrically controlled switch.

In the following diagram, the purple  cylinder, the coil around it and the green shaft make the actual relay. This circuit is used to turn the power on the 'High- Powered motor that is connected to black terminals.

Since the motor work on a dangerously high voltage, it is not sensible to manipulate such a thing directly; so, we assign the job to our invisible hand - the relay. It acts on a very low voltage and poses no threat to those who handle the High- Powered motor.


When the switch is on, the purple cylinder becomes an instant electromagnet and it attracts the green shaft. Then the two black rods come into contact and the motor is turned on.
So, we can handle the motor through the electromagnetic relay.

The following animation shows how it works:


Please answer the following questions.

  1. Discuss the use of electromagnetic relay in various applications.
  2. Describe in detail the mechanism of a circuit-breaker. Discuss the role played by the solenoid in the device. How do you reset it, once activated?
  3. A simple relay circuit is used to activate a burglar alarm that has been connected to a window. Draw an appropriate circuit diagram to illustrate this.
  4. In car factories, relay circuits play a very prominent role. Discuss this.