Question

You are required to make an electromagnet from a soft iron bar by using a cell, an insulated coil of copper wire and a switch. Label the poles of the electromagnet.

Answer 1

An electromagnet is simply a coil of wire. It is usually wound around an iron core. However, it could be wound around an air core, in which case it is called a solenoid. When connected to a current source, the electromagnet becomes energized, creating a magnetic field just like a permanent magnet. The magnetic flux density is proportional to the magnitude of the current flowing in the wire of the electromagnet.
The polarity of the electromagnet is determined by the direction of current. The north pole of the electromagnet is determined by using our right hand. If we wrap our fingers around the coil in the same direction as the current is flowing (conventional current flows from + to -). The direction our thumb is pointing is the direction of the magnetic field, so north would come out of the electromagnet in the direction of our thumb. Above is the circuit diagram of an electromagnet.