Solenoids (Electromagnets)

Electromagnets

An electromagnet is composed of a cylindrical core of ferromagnetic material with N turns of wire wrapped around it, carrying I.

Relay and Contractors

A relay has a moveable arm which once a coil is energized, the N.O contacts are closed and the N.C contacts are open which occurs due to the following force
$F_{magnetic}=\frac{B^{2}A}{2{\mu }_0}$
Where ${\mu }_0$ is a permeability constant
Then, the two pieces get attracted to each other. Once the core is demagnetized, the spring moves the arm back to its original position.