What are magnets?

Magnets can be made by placing a magnetic material such as iron or steel, in a strong magnetic field. Permanent, temporary and electromagnets can be made in this manner.

The atoms forming materials that can be easily magnetized such as iron, steel, nickel, and cobalt are arranged in small units, called domains. Each domain, although microscopic in size, contains millions of billions of atoms and each domain acts like a small magnet. If a magnetic material is placed in a strong magnetic field, the individual domains, which normally point in all directions, gradually swing around into the direction of the field. They also take over neighbouring domains. When most of the domains are aligned in the field, the material becomes a magnet.

Before magnetization


After magnetization

What are temporary magnets?

Soft iron and certain iron alloys, such as permalloy (a mixture of iron and nickel) can be very easily magnetized, even in a weak field. As soon as the field is removed, however, the magnetism is lost. These materials make excellent temporary magnets that are used in telephones and electric motors for example.

What are permanent magnets?

Other kinds of alloys such as alnico (an alloy of aluminum, nickel, iron, cobalt), make excellent permanent magnets. Ferrites (ceramic like materials made of iron oxides with nickel and cobalt) also make excellent permanent magnets. In these materials the domains are more difficult to dislodge, once they are aligned.

What are electromagnets?

Electromagnets are used when really strong magnets are required. Electromagnets are produced by placing a metal core (usually an iron alloy) inside a coil of wire carrying an electric current. The electricity in the coil produces a magnetic field. Its strength depends on the strength of the electric current and the number of coils of wire. Its polarity depends on the direction of the current flow. While the current flows, the core behaves like a magnet, but as soon as the current stops, the magnetic properties are lost. Electric motors, televisions, maglev trains, telephones, computers and many other modern devices use electromagnets.

What are superconductors?

These are the strongest magnets. They don't need a metal core at all, but are made of coils of wire made from special metal alloys which become superconductors when cooled to very low temperatures.

How did it all begin?

There are many legends accounting for the discovery of magnets. One of the most common, is that of an elderly shepherd named Magnes, who was herding his sheep in an area of Northern Greece called Magnesia, about 4,000 years ago. It is said that both the nails in his shoes and the metal tip of his staff became firmly stuck to the large, black rock on which he was standing. This type of rock was subsequently named magnetite, after either Magnesia or Magnes himself.

Stories of magnetism date back to the first century B.C in the writings of Lucretius, and the magical powers of magnetite are mentioned in the writings of Pliny the Elder. For many years following its discovery, magnetite was surrounded in superstition and was considered to possess magical powers, such as the ability to heal the sick, frighten away evil spirits and attract and dissolve ships made of iron! Unlike amber (fossilized tree resin), magnetite was able to attract objects without first being rubbed. This made magnetite far more magical. People soon realized that magnetite not only attracted objects made of iron, but when made into the shape of a needle and floated on water, magnetite always pointed in a north-south direction creating a primitive compass. This led to an alternative name for magnetite, that of lodestone or "leading stone".

Who discovered magnets?

The first attempt to separate fact from superstition came in 1269, when a soldier named Peter Peregrinus wrote a letter describing everything that was known, at that time, about magnetite. It is said that he did this while standing guard outside the walls of Lucera which was under siege. While people were starving to death inside the walls, Peter Peregrinus was outside writing one of the first 'scientific' reports and one that was to have a vast impact on the world. It wasn't until the experiments of William Gilbert in 1600 that significant progress was made in the understanding of magnetism and it was another century or so before other scientists began, by experimentation, to understand the phenomenon.

Who were the scientists who helped us to understand magnets?

It was William Gilbert who first realized that the Earth was a giant magnet and that magnets could be made by beating wrought iron. He also discovered that the induced magnetism was lost if the iron was heated. In 1820, Hans Christian Øersted, demonstrated for the first time (at a public lecture), that there was a relationship between electricity and magnetism.

What is magnetite?

Magnetite is found in rock strata associated with iron deposits and has been found in the ocean floor dating from 2 to 55 million years old. Magnetite is magnetic because its molecular structure has allowed it to retain the alignment of particles caused by the Earth's magnetic field during its formation millions of years ago. When heated to high temperatures magnetite loses its natural magnetism. Not all iron deposits are magnetic, however, which for many years posed a question. Why is magnetite only formed in certain iron deposits? Recently an interesting theory has emerged concerning an anaerobic bacterium, GS-15, which has been shown to convert ferric oxide into magnetite. It is thought that GS-15, could be responsible for the creation of magnetite layers in many iron formations.

What are magnetic force fields?

The area of force (magnetic field) surrounding a piece of magnetite or a bar magnet can be represented (visualized) by the lines of force as shown below, although these lines are no more real than the lines of latitude and longitude on a map or globe.

What is the rule of magnetism?

Like poles repel and unlike poles attract.

Lines of force are three-dimensional, surrounding a bar magnet on all sides.

When opposite poles of a magnet are brought together, the lines of force join up and the magnets pull together.

When like poles of a magnet are brought together, the lines of force push away from each other and the magnets repel each other.

How does a compass work?

The north and south ends of the Earth are called the north and south poles. Because of the Earth's iron-nickel core, the Earth behaves like a magnet. The Earth's magnetic poles are near the geographic poles.

A compass needle is also a magnet, with north and south poles. One pole of the needle is north-seeking and is marked "N", that is, it always points to the Earth's magnetic north pole. Similarly, the other pole of the compass needle, marked "S", is south-seeking and always points to the Earth's south magnetic pole.

The Earth itself acts as a magnet with two poles and an enormous magnetic field. At some places on the Earth's surface, its magnetic force is greater than at others. Moreover, the magnetic strength changes with the passage of the Moon around the Earth. The magnetic poles also shift their positions slightly from year to year. The Magnetic North Pole and the Geographic North Pole do not coincide.

Who first used a compass?

Hundreds of years ago Chinese sailors used pieces of magnetite, made into needles, to help them find their way if they were lost. A piece of magnetite, or a bar magnet, when freely suspended, generally comes to rest pointing in a north-south direction (a compass needle is a magnet). The Earth is like a giant magnet and behaves as if there is a huge bar magnet in the centre.

Digging deeper into terrestrial magnetism

For centuries travellers used compasses for navigation without understanding how they worked. For many years it was assumed that the magnetic and geographic poles were the same, a misconception that led to the early discovery of North America by Christopher Columbus in 1492. At the magnetic poles the field lines point straight up and down and so a compass there is useless.

Like all forms of magnetism the Earth's magnetic field is produced by electric currents. One theory accounting for the production of these currents is that deep in the Earth's core, hot molten magma rises, cools and sinks. Then, the whole process repeats itself. It is thought that within these rising and falling masses of magma the rotation of the Earth creates organized patterns of circular electrical currents, called eddies. The interior of the planet in fact acts like a giant dynamo.

Geophysicists have found that some of the Earth's magnetic field reversals occurred within a few 10,000 years of each other, and others, tens of millions of years apart. Lately the field has been reversing on the average, every 200,000 years, although it hasn't happened in the last 800,000 years. It is not known whether this reversal occurs gradually, or whether there is a period of time when there is no magnetic field at all. This latter possibility could have devastating effects for life on Earth, as it is the magnetic field which protects the Earth from deadly solar radiation. In fact, there appears to be good correlation between magnetic field reversals in the past and extinction of certain species. It is not known why these reversals occur, but it is as if the 'dynamo' in the Earth's core is turned off and turned on again in the opposite direction.

The Earth's magnetic field is also involved in the production of beautiful lights over the north pole called the Northern Lights or Aurora Borealis.

What are some uses of magnets?

The discovery of magnets was very important as they are used to make electric motors and generators. Things that would disappear if we had no electricity are telephones, lights, electric heat, computers, televisions.

Some uses of electromagnets: Maglev trains, car crushers, scrap metal sorters, telephones, computers, doorbells, tape recorders etc. Maglev trains operate without wheels as they 'float' above the track due to magnetic repulsion between electromagnets in the track and underside of the train. Maglev trains can travel very fast, up to 480 km/h (300 mph).

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