Magnetism

Magnetism is a force that can either attract or repel different materials. Electromagnetism is one of the four fundamental forces that govern the universe, along with gravity, strong force and weak force.

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A view of the Earth’s magnetic fieldFondazione Bracco

Without these fundamental forces matter in the universe would break apart and float away. Magnets are objects usually made out of iron and its magnetic properties means that it can exert a force upon other objects without needing to be in physical contact. 

The magnetic field

A magnetic field is the area around a magnetic object which exerts a magnetic force. Magnetic fields cannot be seen but can be illustrated using magnetic materials.

A magnetic field is not related to the force of gravity, gravity is based on the mass of an object whereas a magnetic field is based on what the object is made out of. 

Poles

A magnet has two poles - a north pole and a south pole. These do not exist independently; a north pole is always found with a south pole. Poles of the same type repel each other (eg north and north) and opposite poles attract (eg north and south).

Field lines

Pouring small pieces of iron around a magnet will illustrate the magnetic field. The lines the pieces of irons form are called field lines, these never cross each other.

Magnetic strength

Areas of higher magnetic force will have more field lines closely bunched together. 

Experiment

If you cut a bar magnet in half it creates two smaller magnets with their own north and south pole. 

How magnets work

Magnets have been used for thousands of years however it was only in the 1600’s that scientists started studying how they work. Even today physicists do not have all the answers about the mechanics behind magnetism. 

Atoms

What physicists do know is that magnetism occurs at an atomic level. This is inside an iron atom.

Electrons

In most atoms the electrons zip around the nucleus. All electrons emit a magnetic field but as they are all travelling in different directions these fields cancel each other out. 

Magnet

Inside a magnet however the electrons align all the same way creating a net magnetic field. 

Magnetic domains

When many of these atoms with aligned electrons come together the net magnetic field grows larger and stronger. 

Where Magnets Are Used

Magnets have been used for thousands of years. Naturally occurring magnets were discovered and used by both the ancient Greeks and Chinese 4,000 years ago. 

The first compass (a device that uses the Earth’s magnetic field) was made by the 11th century and continues to be used today. Today magnets can be created and are used in a number of industries. 

Electricity

Electricity can be generated using magnets. Located inside generators these magnets push electrons into wires, creating electrical current. 

Coin detection

Electromagnets are used to detect what kinds of coins are being used in a wide variety of machines. Different coins will affect the magnets differently depending on what metal the coin is made out of and the thickness of the coin. 

Medical

Magnets are used in MRI machines which take detailed images of the human body. The magnets used are at least a thousand times stronger than a normal fridge magnet. 

Recycling

Giant magnets are used at recycling facilities to sort out the different types of metal quickly and efficiently. 

Magnetic materials

Not all metals are magnetic. Metals that can be turned into magnets (and are also attracted to magnets) are called ferromagnetic materials. Examples of ferromagnetic materials include iron, nickel, cobalt and naturally occurring magnets like lodestone. 

Ferromagnetic materials

Ferromagnetic materials are materials normally thought of as magnetic. These metals are both attracted to magnets and can become magnets themselves. 

Paramagnetic materials

Paramagnetic materials such as sodium, tin and aluminium are slightly attracted to one pole of a magnet. This attraction is very weak and can only be measured using specialised equipment.

Diamagnetic materials

Diamagnetic materials such as carbon, water and plastic are weakly repelled by magnets. Again, this force is very weak and can only be measured using specialised equipment.

Earth the magnet

All electrons emit a magnetic field. Due to the Earth’s composition, in particular it’s molten iron core the Earth itself is a weak magnet with two poles. The two poles are located, of course, at the North and South Poles. 

The actual location of the poles move over time, probably due to the continual current changes within the Earth’s molten core. Earth’s magnetic field deflects harmful solar charged radiation away, making the field essential for life on Earth. 

Molten core

Deep inside the Earth is a liquid iron core around two thirds the size of our Moon. Iron is a ferromagnetic material.

Earth’s magnetic field

The Earth’s magnetic field extends from inside the Earth into space. It is thought to be created by the electrons in the Earth’s molten core.

Magnetic North

A compass points towards the Earth’s magnetic North Pole (as opposed to its geological North Pole). 

Switching poles

The movement of the poles can be quite significant and is believed to be linked to the direction of molten liquid in the Earth’s core. Earth’s poles have switched many times, the last time this occurred was 780,000 years ago.

This would mean that compasses would point south instead of north (among other things!).

Electromagnets

The main difference between magnetism and electromagnetism is the addition of electricity. Adding electricity to a magnet can change the way the metal behaves when compared to a permanent magnet like a fridge magnet. 

It is easy to make an electromagnet yourself using a few common household items.

Creating an electromagnet

To make an electromagnet wrap some copper wire around an iron object like a nail. Attach the ends of the wire to a battery to introduce electricity.

Electricity

Flowing electricity around the iron object magnetises it. As long as the electricity is flowing the iron remains magnetised. If the electricity is removed the magnetism stops. 

Control

Electromagnets are very useful as it is easy to control the strength of the magnet. Changing the amount of electric current will change the strength of the magnet. Poles can also be reversed by reversing the flow of electricity.

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