In the modern world, we use magnets in an overwhelming number of different ways. From the way that a fridge door closes to the way in which your headphones play music, from the generation and transmission of electricity, to the motor in your car. All of these use magnetic force in some way or another.
Given the current ubiquitousness of magnets, our particular civilisation would be a bit useless without them. We’d have no way to move electric currents across the country. All of our electric motors would be useless. And we wouldn’t be able to talk across distance – as we have become so used to doing.
As such, we shouldn’t take these particular things for granted. Rather, we should – all of us, that is, not just the scientists – try to understand what they are all about: how they work, what the special relationship is between electricity and magnetism, and how they make our world go around.
This is our special task in this series of articles: to allow everyone to understand why it is that electrons have a magnetic moment, say – or why an electric current might produce a magnetic field. Why it is that magnetic flux can induce an electric charge, or why all of this stuff is so important for our world.
Let’s take a look – from the basics of the magnetic field to the most important of the magnetic technologies.
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How to define magnetism
Let’s start with magnetism.
Magnetism is the force, present in and between all objects, that is produced by the motion of electrons – and that results in the attraction and repulsion of different objects. It is a ‘noncontact’ force that affects every single different object in the world, to a greater or less extent, and that is the result of the movement of these subatomic particles, electrons, and their electric charge.
Electrons, Magnetic Moments, and the Three Types of Magnetism.
Every atom in a substance is made up of particles, including the neutrons, electrons, and protons. In magnetism, it is the electrons that are doing the work.
These tend to orbit the neutrons, and they each have their own charge – either positive or negative. What generally happens is that the electrons ‘pair’ with those of an opposite charge – meaning that an electron with a negative charge would pair with one that is positive – and so the material would be relatively stable, as each of the charges would cancel the other out.
When substances have paired electrons, we refer to it as diamagnetism.
However, there are plenty of types of materials – including oxygen – that have unpaired electrons. When this happens, the substance becomes much more magnetic, as the electrons can all align. In most of these materials, however, they do not, as the ‘magnetic moments’ of each of these individual electrons are not equal – unless they are under the influence of an external magnetic field.
These substances which only demonstrate magnetism when they are in an external magnetic field we call paramagnetic.
And, finally, there are the ferromagnetic substances. These are the magnetic materials which have unpaired electrons of the same magnetic moment. This means that, spontaneously, they can become magnetic – and they will remain magnetic even after the removal of an external magnetic field.
What, then, is the Magnetic Field?
Every magnet or magnetic object has a magnetic field – the neighbourhood around the magnet in which its magnetic force is present. It is the space affected by the magnet’s magnetic charge.
Permanent magnets and electromagnets have enduring magnetic fields, which you will conventionally see with iron filings that arrange themselves into the shape of the magnetic field lines. These will follow the flow from the magnet’s north pole to its south pole.
Magnetic fields change depending on the strength of the magnet.
Find out more about magnetic fields!
What is an Electromagnet?
Apart from the magnetic moments of the electrons, the other thing that produces magnetic fields are electric charges. This discovery, back in the 1830s, has been one of the most important in history, as it created the link between magnetism and electricity.
We’ve just seen that electrons in a substance have a magnetic charge – due to the fact of their movement within the magnetic material.
But the place in which electrons really move is in electric currents, which, really, are just the movement of electrons. As currents move down a wire, the wire becomes magnetized as the movement of the electrons produces the magnetic field.
It was André-Marie Ampère who discovered this, as he showed that parallel wires would attract or repel each other, depending on which way the current would pass. (He would later give his name to the amp or ampere, by the way.)
How to Make an Electromagnet.
Since the very earliest electromagnets, the technology has not changed very much. They have become stronger, yes, but the overall structure of the devices has remained the same.
Electromagnets are made of a coil of wire, wrapped around a core of metal (usually a ferromagnetic material like iron). Into the coil of wire is passed an electric current, whose magnetic field is centred into the hole in the coil – i.e. the iron core. This whole structure is known as a solenoid – and is still used in all of the places where electromagnetism is in action.
As soon as the electric current is switched off, the solenoid ceases to be magnetic.
A Note on the Relationship between Magnetism and Electricity.
Whilst we know that electricity produces a magnetic field, and that magnetic fields rely on electrons, the distinction between a thing called magnetism and a separate thing called electricity is a false one.
These are not discrete forces. Rather, they are the same physical principle – like two sides of the same coin. ‘Electromagnetism’ as a thing is actually one of the fundamental forces in the universe.
You find out more about electromagnetism in our dedicated article.
What is Electromagnetic Induction?
One of the most useful discoveries in the history of electromagnetism was made by Michael Faraday, a British scientist in the nineteenth century. This became known as electromagnetic induction – and it remains one of the core parts of our knowledge of electromagnetism to this day.
Faraday’s experiments focused on the way that electric charges can be manipulated by magnetic fields. And he surmised that changes to a magnetic field can be used to induce an electrical current.
This sounds complicated, but his actual practical experiments were fairly simple. He took an iron ring and wrapped two different wires around opposite sides of the ring – producing two solenoids on the same piece of iron.
Attaching one piece of wire to a battery, he attached another to a galvanometer, a machine which measures electric charges. Connecting and disconnecting the first wire from the battery produced a change in the charge detected by the galvanometer. This, for Faraday, proved that the change in the magnetic field in the iron ring could induce an electrical current on the separate wire.
To prove his ideas about this particular relationship between electricity and magnetism, he did another experiment. Taking a solenoid without a core (so just a wire coil), he inserted a bar magnet in and out of the coil. Pushing the magnet faster, he found a larger current was produced in the wire.
Why was this so important? Because Faraday paved the way for the knowledge that electrical currents don’t only flow through wire – whilst he set the theoretical ground on which we came to produce electrical energy by manipulating its magnetic field.
Learn more about electromagnetic induction!
What is a Transformer?
Transformers are the crucial piece of technology that use the science of electromagnetic induction.
They are perhaps the most common electrical devices on the planet, with almost the entirety of electrical energy that we produce and use passing through at least one transformer in its journey.
So, what are transformers? A transformer is a static device that changes a current of a high voltage into one of a much lower voltage. It does this through the presence of two adjacent solenoids and through Faraday’s electromagnetic induction.
Across the country, electricity is transmitted through massive electrical networks. But to keep costs down, the electricity that is transported is of super high voltages. This – rather than a high current – reduces wasted energy and means that the wires themselves don’t need to be big.
However, we can’t actually use high voltage electricity. So, before the electricity is distributed locally into our homes, it needs to be transformed into lower voltage electricity. That’s what transformers are for.
Reducing Current Voltage.
Faraday’s law shows how electromagnetic induction can be used to reduced and increase the voltage of electrical currents.
Think back to his experiment: he used two different coils, in which the changes in magnetic field between the two induced an electrical current in the second.
If, however, you vary the number of coils in the wire, you can change the voltage of the current induced. Say you have ten coils on the first wire, you can simply halve the number of coils on the second and you have half the voltage.
This is precisely how transformers work.