Question

how to increased strength of electromagnet.

Answer 1

Putting a piece of iron or steel inside the coil makes the magnet strong enough to attract objects. The strengthof an electromagnet can be increasedby increasing the number of loops of wire around the iron core and byincreasing the current or voltage.

Answer 2

The strengthof an electromagnet can be increasedby increasing the number of loops of wire around the iron core and byincreasing the current or voltage.
Hope it help you.