Magnetite

This iron oxide mineral, also known as lodestone (translated as ‘course stone’), was once used as a primitive compass, as it can be found naturally magnetised.

Pyrrhotite

The most common naturally magnetic mineral after magnetite, some pyrrhotite specimens have a weak amount of magnetism, enough to attract a paper clip.

Hematite

Often considered to be non-magnetic, atoms within a hematite crystal are seen to align with one another very slightly, indicating a tiny magnetic force.

Earth

The Earth acts as a magnet due to electric currents in the core, similar to an electromagnet, but its magnetic field is 100 times weaker than a fridge magnet.

Magnetar

Often referred to as the most powerful magnet in the universe, if this rotating star came within 100,000 miles of Earth it would wipe every single one of our credit cards. Of course, the repercussions of an object this massive being close to Earth, other than the magnetic forces, would probably be much more devastating… There’s no need to worry, though, as the nearest one is 13,000 light years away.

The strength of a magnet is most commonly measured using a magnetometer, also known as a gaussmeter, which are used to measure everything from the Earth’s magnetic field to small magnets. A magnetometer consists of a small conductor or semiconductor at the tip of a probe through which an electrical current is passed. The effect of the magnetic field on the electrons in the conductive material can then be measured. The International System unit for measuring magnetism is the tesla which measures something called the magnetic flux density, but teslas are only really useful for measuring very large magnetic fields.

A more suitable way to measure smaller magnetic fields is to use the unit gauss. One tesla equals 10,000 gauss. The Earth’s magnetic field is about half a gauss, a fridge magnet about 100 gauss and a large electromagnet like that in a MRI could be up to 1,500 gauss. There are several factors that will affect the results of any measurement such as the distance from the magnet the reading is taken, the magnet’s size and whether or not the magnet is attached to anything. A more practical measure of a magnet’s strength is to measure how much weight it can lift.

Connor Skates, Science Museum

We all know that if we put two magnets next to each other with opposing north poles they repel each other. Indeed, this principle is in use today for commercial purposes, as can be seen in the high-speed floating maglev trains of China and Japan. However, when a magnet is put opposite a super-cooled superconductor then it levitates, as can be seen in the video. But why is this?

Superconductors work as, when cooled to a certain point, they lose all electrical resistance. This near absolute zero temperature causes atoms to cease random vibrations, thereby allowing un-impeded flow for its electrons and a total loss of electrical resistance. The Meissner effect is a common property of these zero electrical resistant superconductors. It works because the magnet’s magnetic field cannot penetrate the superconductor, causing its lines of force to be expelled back at it. This has the effect of creating a mirror-image of the magnet within the superconductor and, through the expelled lines of force it is creating, causes itself to levitate.

When watching the video you can see this in action in real time. Notice how at the start of the experiment the magnet remains stationary against the superconductor in the centre of the white slab. It is only then when liquid nitrogen is poured over the superconductor and electrical resistance is removed, does the mirror-image Meissner effect then take place, causing the magnet to levitate above it. At the end of the experiment, when the superconductor is removed from the slab of liquid nitrogen, the magnet then slowly falls back to earth as the flow of electrons is once more impeded as temperature returns to normal.

Interestingly, there is huge potential for superconductors in the real world. For example, when electricity is passed upon power lines in order to power our homes and places of work, then the further from the source it reaches (i.e. remote farms and villages etc) then, thanks to the resistance caused in the metal line by the vibrating atoms, a certain proportion of this electricity is lost. This inefficiency means that it costs more money and more power to send electricity long distances. Just imagine though if all electrical resistance could be eliminated in the power lines, as in superconductors? Then electricity could be passed almost for free over any distance and, if transferal methods were redesigned to allow the electricity to circulate along a coiled wire, then electricity would circulate for millions of years without any reduction in energy.

Of course all this would require either the the power lines to be submerged in liquid nitrogen which is impractical or, and far more realistically, a superconductor be created that has zero electrical resistance at room-temperature – something which scientists are working feverishly to realise.