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

# Three Pole Magnet

## Introduction

Everyone knows that a permanent magnet has two poles, north pole and south pole. Their strengths are supposed to be same. Some texts go further stating that for a bar magnet, the ``magnetic length'' is 0.84 of the physical length of the magnet. However all this can be very different depending on how you magnetize the bar. In this experiment, you will make a magnet that will have three poles, instead of two.

## Apparatus

A bicycle spoke, two bar magnets, a compass.

## Procedure

1. Place the bicycle spoke on horizontal surface and hold it tight.
2. Take two bar magnets in two hands, both north poles (or both south poles) down. Put then in contact with the spoke at the middle.
3. Pressing the magnets against the spoke, slide them on the spoke so that the magnets reach opposite ends of the spoke. Your 3-pole magnet is ready.
4. Place a compass on the surface and bring one end of the spoke near the compass. Which end of the compass is attracted to the spoke?
5. Now bring the other end of the spoke close to the compass. Which end of the compass sets attracted to the spoke? Is it the same end which is attracted to both ends of the spoke.
6. Now bring the middle portion of the spoke close to the compass. See that the compass deflects. Which end of the compass gets attracted to the spoke?
7. Is the pole appearing the middle of the spoke similar or opposite to the poles at the end?