It is great fun to play with magnets, to feel the force they exert being attracted to metal objects, and repelling each other when placed the wrong way round. This is because they have what is called a “North pole” and a “South pole." The North pole of a magnet will always be attracted to the South pole of another magnet, and repelled away from another magnet’s North pole.
But magnets also play a very important role in many modern electrical and electronic devices. Magnetism is an incredibly useful force, because of the way that it interacts with electric currents. There is a whole area of study called ‘electromagnetism’ that looks at how magnets, electric currents and movement are connected.
Scientists usually refer to magnetic energy as a ‘magnetic field’, which is an invisible area of influence that magnets have all around themselves. The further away from the magnet you go, the weaker that field becomes. That field can be felt if you hold a metal object near the magnet – the field pulls the metal object towards the magnet (or, conversely, the magnet towards the metal object!).
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Examples of Magnetic Energy
Magnets can be either ‘permanent magnets’ – this means they are magnetic naturally and keep their magnetism all the time. Or they can be ‘electro-magnets’. Electro-magnets are not naturally magnetic, but when you pass an electric current through them, they become magnetic.
There are many different kinds of equipment that rely on magnetic fields to operate, but here is a list of the most common examples:
Electric motors
Electric motors are used in many applications – electric vehicles (EVs), fans, pumps, hair dryers, vacuum cleaners, food processors, air conditioners, blu-ray disc players – any electrical device that has something in it that spins round is sure to have a motor in it.
There are a number of different types of electric motor, but they all need magnets to work. Due to a special effect called electromagnetic induction, when an electric current is passed through a coil of wire that is inside a magnetic field, it makes the coil want to move in time with the current. Motors work because that moving coil is attached to an axle that spins within the magnetic field, creating a rotating output shaft from the motor that can be used to drive anything.
Compass
A compass is a device that indicates the direction of the north pole of the earth from where you are standing. They have a circular background marked with “North”, “East”, “South” and “West” indicated going round the edge. They have a magnetised metal pointer in the middle that spins freely on a central pin. The earth gives off a very weak magnetic field, and it is this field that the compass pointer can detect. When left to settle, it will always point towards the magnetic north pole of the earth.
Loudspeakers
Loudspeakers receive an electric signal from an amplifier, and convert it into sound. Some loudspeakers do this by using magnets. The sound comes from a shallow cone that is attached to a coil of wire sitting inside a permanent magnet. When an electrical signal is fed into the wire coil, electromagnetic induction makes the coil want to move in time with the electrical signal. Because the coil is attached to the speaker cone, the cone also moves back and forth, creating sound waves that we can hear as music or speech or whatever sound is being sent down the wire.
Hard disk drives
Hard disk drives are used to store programs and data on computer systems. They are small boxes, usually about 3 or 4 inches across by about an inch deep. Inside, they have a stack of very thin circular metal discs, called platters, and the surfaces of these platters are treated with a magnetically sensitive material. A thin metal arm slides in between each platter, and at the end of this arm is a magnetic “head”. The head can be electrically magnetized with either a north pole or a south pole.
Computers record all their data on hard disks in binary – 1s and 0s. When the computer wants to write data to the hard disk, it magnetizes the head with a north pole to indicate a binary “1” and a south pole for a binary “0”. As the disk spins round, the head changes from north to south and this stream of data is recorded as microscopic magnetic north pole and south pole spots on the surfaces of the platters.1
Then, when the computer wants to read the data back from the hard drive, the arm goes into reading mode, and senses the north and south pole spots on the surface of the disk, sending a stream of binary 0s and 1s back to the computer for decoding.
This is why you must be very careful not to put a computer hard disk drive too near a powerful magnet. The magnet would ‘erase’ all the north and south pole spots on the platters, and whatever data was on the disk would be lost forever.
Generators
A Generator is essentially an electric motor that is being used in reverse. In a motor, an electric current is sent into the motor, causing the motor spindle to rotate. In a generator, the spindle is rotated by an external force, which creates an electric current that comes out of the generator. There are enormous generators used inside all power plants (e.g., nuclear, hydroelectric, wind turbines etc) and these are what generate the electricity that is sent to homes and places of work across the country. So without magnets, you can quite truthfully say you would not be able to switch on your lights at home!
MRI Scanners
An MRI scanner is a large, cylindrical machine that hospitals use to scan patients to help doctors diagnose various medical conditions. The patient lies on a thin, flat bed, and they are slowly slid through the central hole in the centre of the machine. As they move through, the scanner takes “pictures” like a series of slices of their insides. MRI stands for “Magnetic Resonance Imaging”. Hugely powerful electromagnets inside the scanner create a very strong magnetic field at the centre of the cylinder, and as the patient moves through this magnetic field, the machine can take readings from inside their body, because different parts of their body (e.g., bone, muscle, tissue, fluids etc) react differently to the magnetic field. This process builds up a very detailed image that doctors can then use for diagnosis.
Maglev Trains
Maglev is an abbreviation of ‘magnetic levitation’. A maglev train has no wheels – it hovers over the train track, suspended by very powerful opposing magnetic fields (e.g., north to north or south to south) created by superconducting electromagnets. When cooled down to a very low temperature (about -450 degrees Fahrenheit) these electromagnets exhibit a special effect called superconductivity, which means they have zero electrical resistance and can create hugely powerful magnetic fields – enough to lift the weight of a train.2
Maglev trains also use the attraction and repulsion of the north and south poles of magnets to push and pull the train along the track, and they can achieve very high speeds indeed since there is no friction between the train and the track. The fastest maglev train in the world is currently in development in China, and it has a top speed of approximately 370 mph.3
