How will you make a bar of iron an electromagnet ? Draw a diagram showing the polarities of an electromagnet.

A bar magnet can be made electromagnet with the following method :

Electrical Method :

Take the given iron bar AB. Wound several turns of insulated copper wire over the bar. Connect the ends of the wire to a battery through a switch as shown in below figure.

Press the switch to pass current. After some time, the bar AB becomes a magnet. The end A of the bar at which the current enters the coil in clockwise direction becomes the south pole (S) and the end B of the bar becomes the north pole (N). The polarity at the ends of the bar can be reversed by reversing the direction of current in the coil.