What is an Electromagnet?

An electromagnet is a type of magnet in which the magnetic field is produced by an electric current. Unlike a permanent magnet, the strength of an electromagnet can be easily changed by changing the amount of electric current flowing through it. The poles of an electromagnet can be reversed by reversing the flow of electricity.

How to build an electromagnet?

It is fairly easy to build an electromagnet. All we need to do is wrap some insulated copper wire around an iron core. If a battery is attached to the wire, an electric current will begin to flow and the iron core will become magnetized. The magnetic field is perpendicular to the field of the electric current. If we want to make the magnet stronger, then we wound the coil more around the core. The more electric charge the battery has, the stronger the electromagnet is. When the battery is disconnected, the iron core will lose its magnetism. 

How to determine polarity of the electromagnet?

The electric current goes from the positive side to the negative side. We use a right-hand thumb rule to determine which side is north and which side is south.The right-hand thumb rule states that if you curve your hand in the way the coil has been wound and stick out your thumb, the direction your thumb is facing is the north side of the magnet.