Give information about electromagnets.

Explanation

It is known as the electromagnet that only have magnetic property until the electric current from the ferromagnetic material is passed.
Core of electromagnets are made of ferromagnetic materials.
These materials have high permeability and low retentivity. So soft iron is a suitable material for electromagnets.
On placing a soft iron rod in a solenoid and passing a current, the magnetism of the solenoid increased by thousand fold.
When we switch off the solenoid current, the magnetism is switched off because the soft iron core has a low retentivity.

In transformer core and telephone diaphragms, the material goes through an ac cycle of magnetisation for a long period. The hysteresis curve of such materials must be narrow, so the energy dissipated and the heating will be small.
The material must have high resistivity to lower eddy current losses.
Uses of electromagnets : Electromagnets are used in electric bells, loudspeakers and telephone diaphragms.
Giant electromagnets are used in cranes to lift machinery and bulk quantities of iron and steel.