What is the principle of electromagnetic relay?

The relay is an electromechanical switch. It is an enamelled copper wire wound on a round iron core for several hundred to several thousand turns. When a current flows through the coil, the round iron core generates a magnetic field, and the upper side of the round iron core is provided. The iron plate of the contact piece is attracted to open the first contact and the second switch contact. When the coil is de-energized, the core loses its magnetic properties, and due to the elastic action of the contact copper piece, the iron plate leaves the iron core and resumes connection with the first contact. Therefore, it is possible to control the switches of other circuits with a small current. The entire relay is protected by a plastic or plexiglass dust cover, and some are fully sealed to prevent electro-oxidation.
As shown in the figure above, when the switch K in the control circuit is closed, the electromagnet is magnetic, the armature is sucked down, the relay contacts are contacted, and the power supply circuit connected to the contact is turned on; when the control switch K is disconnected When the magnet's magnetism is removed, the relay contacts pop open and the power circuit is disconnected.