1.01 Introduction to magnetism

The first applications of magnets were as navigation devices. When naturally occurring magnetic rocks were freely suspended they would always rotate to a particular direction. These rocks were called lodestones (from the word lode which means way or journey). The rock was used to magnetise a needle. The needle was then placed on a piece of wood floating on water. This allowed it to rotate to indicate the direction of the north pole. Chinese sailors were among the first to make use of these devices for navigation. These rocks also had the ability to attract some types of metallic objects but at the time their application for navigation was far more significant. We now know that the properties of lodestones are due to magnetised metallic particles in the rock.

Load Stone

Observed properties of magnets

Consider a simple bar magnet as shown below. The opposite ends of the bar magnet are named north and south poles from the directions they point when freely suspended. If two bar magnets are brought together with a north and south pole facing the magnets will attract each other. If they are brought together with either two south or two north poles facing each other the magnets will repel each other. Like poles repel, opposites attract.

Bar magnet