IIT JEE Physics (1978-2018: 41 Years) Topic-wise Complete Solutions

# Making of an Electromagnet

## Objective

To explore the magnetic effect of an electric current.

## Introduction

An electromagnet is made by passing electricity through an insulated wire wound around a soft iron core. When an electric current is passed through a wire, the soft iron core becomes magnetized. It looses its magnetic properties as soon as the flow of electric current is switched off. The strength of an electromagnet depends upon the number of turns in the coil, the strength of current through the coil, and the properties of the core material.

## Apparatus

thin insulated copper wire, long iron nail, magnetic compass, iron pins.

## Procedure

Wind a solenoid directly over an iron bolt or nail, using 5-8 feet of thick enamelled copper wire. (In these wires, the enamel coating acts as an insulator.) Use adhesive tape to keep the turns in place. Remove the enamel from the free ends of the wire, and connect them to a battery through a switch. Now, close the switch. The bolt will attract iron and steel objects placed near it. If you turn the current off, the bolt will no longer attract these objects.

## Discussion

Test the strength of the electromagnet by attaching pins one below the other. Wrap one or two extra layers of the coil over the first one and test the strength again. Bring the electromagnet near a compass to test its polarity. Change direction of current and again test its polarity.

Now connect the electromagnet to two or three batteries in series and see the strength. Remove the batteries and see what happens.

The soft iron core makes a stronger electromagnet as it can be magnetized easily. The polarity of electromagnet depends on the direction of flow of current.

## Note

Hazard: Never connect the coil to the 220 V supply. It may be fatal.