99 Fun Facts About Magnets

The word magnet comes from a Greek term meaning a stone from which ancient place?

Magnesia also gave English the words magnesium and manganese; whether the 'Magnesian stone' came from the district in Thessaly or a namesake city in Anatolia is still argued.

Lodestone, the first compass material, is a naturally occurring form of which mineral?

Magnetite that has become magnetised is called lodestone, an old word meaning 'way stone', because it was used to make the compass needles that guided sailors.

Which three elements are the classic ferromagnetic metals strongly attracted to a magnet?

Iron, nickel and cobalt have a part-time fourth member: gadolinium is ferromagnetic too, but only below about 20 °C, so it drops out on a warm day.

What do you get if you snap a bar magnet in half?

You get two complete magnets, each with its own north and south pole, however many times you cut; nobody has ever isolated a lone magnetic pole, though physicists keep looking.

What happens to an iron magnet heated past its Curie point, about 770 °C?

It stops being magnetic because heat jostles the tiny aligned regions inside it out of step; for iron that happens far below its melting point of about 1,500 °C.

Which Curie's doctoral work on magnetism gave the Curie point its name?

Pierre Curie finished that doctorate in 1895, the year he married Marie; within three years he had dropped his own research to join hers on radioactivity.

The magnetic compass is usually traced to which Chinese dynasty, a contemporary of ancient Rome?

Han diviners are credited with a lodestone spoon whose handle swung round to point south on a bronze plate; Chinese sailors took up the compass only about a thousand years later.

Which Song dynasty polymath gave the first known description of a magnetic compass needle?

Shen Kuo described it in his Dream Pool Essays, written in seclusion in his last years; the book also argued from seashells found in mountain rock that the land there had once been a seashore.

On a compass card, which direction corresponds to a bearing of 90 degrees?

East is why a runway numbered 09 faces that way: runway numbers are compass bearings with the last digit dropped, so runway 27 points west.

Which British inventor built the first electromagnet in the 1820s?

William Sturgeon wound bare copper wire round a varnished iron horseshoe; fed by a single battery cell, the seven-ounce magnet could lift nine pounds.

What can an electromagnet do that a permanent magnet cannot?

Be switched off: its pull lasts only while current flows through the coil, which is how a scrapyard crane can pick up a load of iron and then simply let it drop.

Which Danish scientist discovered in 1820 that electric currents create magnetic fields?

Hans Christian Orsted showed that a live wire swings a nearby compass needle; the same restless experimenter was the first to isolate piperine, the compound that gives pepper its bite.

Which English scientist showed in 1831 that a moving magnet can generate an electric current?

Michael Faraday left school early and learned his science as a teenage bookbinder's apprentice, reading the books he bound; his coil-and-magnet discovery is how power stations still make electricity.

William Gilbert's 1600 book arguing that Earth itself is a magnet was titled what?

De Magnete overturned the older idea that the Pole Star, or a great magnetic island in the far north, was what pulled a compass needle north.

William Gilbert, who showed that Earth is a magnet, was personal physician to which Tudor monarch?

Elizabeth I took him on in 1601 and her successor kept him, but he died in 1603, probably of plague; he is also credited with coining the Latin word, meaning 'like amber', behind 'electricity'.

William Gilbert studied magnetism on a spherical lodestone, a model Earth he called what?

The terrella, Latin for 'little Earth', let him move a tiny needle over its surface and watch it dip just as compass needles do at different points on the real planet.

Neodymium magnets were developed independently in the early 1980s by Sumitomo Special Metals and which carmaker?

General Motors and Sumitomo each worked in secret, unaware of the other, until their two project leaders surprised each other by announcing the same magnet at one conference in Pittsburgh.

A neodymium magnet is an alloy of neodymium, iron and which third element?

Boron completed an alloy whose inventors were only trying to make something cheaper than the costly samarium-cobalt magnets of the day; it turned out to be the strongest permanent magnet on the market as well.

Farmers feed a smooth, finger-sized magnet to which animals to protect them from swallowed nails and wire?

Cows gulp their feed in big mouthfuls, scraps of metal and all, and a sharp piece can pierce the stomach wall; a 'cow magnet' sits in the stomach and holds the metal safely in place.

Most flexible fridge magnets are magnetised in a special pattern called what?

A Halbach array piles the field up on one face of the sheet and nearly cancels it on the other, which is why the printed side of a fridge magnet will barely cling to the door.

Earth's magnetic field is generated by churning molten metal in which of its layers?

The outer core is the one layer that is both metal and liquid: it churns in turbulent convection, working like a naturally occurring electrical generator.

Since it was first located in 1831, Earth's north magnetic pole has drifted from Arctic Canada toward which region?

Siberia is where it is heading, at tens of kilometres a year: fast enough that the navigation model built into virtually every smartphone has to be redrawn every five years.

Picture Earth as a bar magnet: what lies beneath the Arctic, where a compass's north end points?

A south magnetic end lies under the Arctic, because opposite poles attract: a needle's north end can only be drawn to a south pole. The 'north magnetic pole' is named for geography, not physics.

Reversals of Earth's magnetic field happen at irregular intervals averaging how long?

Several hundred thousand years is only the average: the flips come at random, and the last one was about 780,000 years ago, so every compass in human history has pointed the same way.

Lava locks in the direction of Earth's magnetic field when it does what?

Cools: as lava cools, its magnetic minerals record the direction of Earth's field at that moment, so the spreading sea floor preserves a record of past reversals.

The 2007 Nobel Prize in Physics honoured giant magnetoresistance, the discovery that let which devices shrink dramatically?

Hard disk drives read their data with a head built on the effect, found in 1988 by Albert Fert and Peter Grünberg; its sensitivity is what let disks shrink to fit laptops and music players.

One tesla corresponds to how much in the older CGS unit?

The gauss is not accepted for use with SI units under NIST guidelines, though it still shows up on magnet spec sheets.

A typical 1.5-tesla hospital MRI scanner is roughly how many times stronger than Earth's magnetic field?

30,000 times: Earth's field is a feeble 50 millionths of a tesla. The scanner's is strong enough to turn loose steel objects into projectiles, which is why metal is kept out of the room.

Which American chemist made the first MRI image, of two tubes of water, and shared the 2003 Nobel Prize for it?

Paul Lauterbur's paper on the method was at first rejected by the journal Nature; he added a note on its medical promise, and the editors later ranked it among their most influential of the century.

Which liquefied gas, boiling at 4.2 kelvin, cools most superconducting magnet windings?

Helium is cold enough, as a liquid, to make the coil's wire superconduct: current then flows through miles of winding with no resistance, so a huge field costs almost no power to keep up.

The superconducting wire in most MRI magnets is an alloy of niobium and which other metal?

Titanium alloyed with niobium is the workhorse superconductor: building the Large Hadron Collider took so much of the wire that world output doubled for five or six years.

The 603 km/h train speed record was set in 2015 by an experimental maglev from which country?

Japan's L0 Series floats about 10 cm above its guideway on superconducting magnets, so at speed nothing touches the track and no wheel friction holds it back.

The maglev line linking Shanghai to its main airport was built with whose technology?

German engineers at Siemens and Thyssenkrupp developed the Transrapid system on a test track at home, yet the Shanghai airport line remains the only commercial one ever built.

The first commercial maglev people mover opened in 1984 near which English city?

Birmingham's maglev floated passengers the 600 metres from the airport to the railway station for 11 years; it shut in 1995, and a cable-hauled shuttle now runs in its place.

Which planet has the most powerful magnetic field in the Solar System?

Jupiter makes its field in a deep layer of hydrogen squeezed until it conducts like a metal; the field traps particles in radiation belts intense enough to damage visiting spacecraft.

Which physicist showed in 1931 that magnetic monopoles would explain why electric charge comes in fixed units?

Paul Dirac's monopole has never been found, despite decades of searching. He spent his last years at Florida State University, where the national magnet laboratory now stands on Paul Dirac Drive.

A magnetar is an extremely magnetic type of which object?

A neutron star of this kind is the strongest magnet known: park a magnetar halfway to the Moon and it could wipe the data from every credit card on the planet.

Most observed magnetars rotate once every how long?

Ordinary pulsars spin one to ten times per second. As of 2021, 31 magnetars were confirmed out of about 3,000 known objects of their type.

Migratory birds are thought to sense magnetic fields using which protein in the eye?

Cryptochrome is thought to form short-lived pairs of molecules when light hits it, letting a bird in effect see the field; the sense is so delicate that radio and TV broadcast signals can jam it.

Which doctor's 'animal magnetism' cures, first tried with magnets in 1770s Vienna, gave English a word for spellbinding someone?

Franz Mesmer left us 'mesmerise', but not his magnetic fluid: in 1784 a French royal commission headed by Benjamin Franklin tested the cures and found no such fluid, only imagination.

Which caged songbirds lost their sense of magnetic direction in a university lab until their huts were shielded from stray radio noise?

European robins hop the way they want to migrate, but in the campus huts they hopped at random; lining the walls with grounded aluminium sheet brought their compass straight back.

The southern hemisphere's counterpart to the aurora borealis is known by what name?

Aurora australis, the 'southern dawn', exists because Earth's magnetic field guides the Sun's particles to both ends of the planet at once, so each magnetic pole wears its own ring of light.

Which astronomer used the term aurora borealis in his writings in 1619?

Galileo Galilei's 1619 use is the earliest known, though dictionaries long credited the phrase, Latin for 'northern dawn', to the French scholar Pierre Gassendi, who watched a great display in 1621.

The most common green auroral light comes from excited atoms of which element?

Oxygen makes both the common green and, in the thinner air higher up, the rarer red; nitrogen adds the pinks, purples and blues along an aurora's lower edge.

Which Greek philosopher did Aristotle credit with the first scientific discussion of magnetism?

Thales of Miletus, Aristotle reports, reasoned that a lodestone must have a soul, because it can make iron move.

Which Roman author described lodestones and their pull on iron?

Pliny the Elder was a naval commander as well as a writer on nature; in AD 79 he launched ships across the Bay of Naples to rescue people from erupting Vesuvius and did not return, as his nephew recorded.

What natural event is thought to give lodestones their magnetism?

Lightning strikes carry a brief but very strong magnetic field; Earth's own is too weak for the job. A NASA scientist backed the theory by magnetising the right kind of rock at a lightning research lab.

Which weak form of magnetism let scientists levitate a live frog?

Diamagnetism makes water push feebly away from a magnet. Andre Geim floated droplets, then strawberries, then a frog; it won him an Ig Nobel Prize in 2000, ten years before his real Nobel.

Which property of a piece of steel decides whether it stays magnetised once the magnet is taken away?

Coercivity is resistance to being demagnetised: hard steel alloys have plenty and make permanent magnets, while soft iron has so little that it suits transformer cores, which must reverse constantly.

Farmers feed a finger-sized magnet to which animals to trap swallowed nails and wire in the stomach?

Cows swallow stray metal with their feed, so a calf is given a smooth magnet that settles in its stomach for life and stops sharp scraps piercing the gut wall or the heart sac.

Ferrofluid, the black liquid that bristles into spikes near a magnet, was invented in 1963 at which organisation?

NASA engineer Steve Papell wanted a rocket fuel that a magnet could pull toward the pump in weightlessness, and the same liquid now seals the spinning shafts inside hard disks.

The US Mint's 1943 pennies stick to a magnet because they were struck in steel to save which metal for the war?

Copper was needed for ammunition, so the 1943 cent became the only regular US coin a magnet can pick up, and the magnets vending machines used to catch steel slugs caught it too.

Magneto, the Marvel villain who bends metal with magnetic fields, first appeared in 1963 as the enemy of which team?

The X-Men met him in their very first issue, by Stan Lee and Jack Kirby, and later stories made him a former friend of the team's leader, Professor X.

The leading theory says natural lodestones pick up their magnetism from the intense fields around which natural event?

Lightning strikes can magnetise the rock in an instant, which fits the odd fact that lodestones are mostly found near the surface and not buried at great depth.

Which planet's air has been thinned by the solar wind since its global magnetic field died about four billion years ago?

Mars has only patches of magnetised crust left, and with no global field to funnel particles to the poles its auroras can glow across the whole planet.

The 1859 Carrington Event, the most intense geomagnetic storm on record, set fire to which Victorian technology?

Telegraph stations picked up so much storm-driven current that operators in Boston and Portland unplugged their batteries and talked for two hours on the aurora's power alone.

Which Vienna doctor's 1770s theory of "animal magnetism" gave English a word for holding someone spellbound?

Franz Mesmer first tried magnets on a patient in 1774, but a French royal commission blindfolded its subjects in 1784 and found the cure only worked on people who knew it was happening.

Which type of kitchen hob only heats pans that a fridge magnet will stick to?

Induction hobs use a fast-changing magnetic field to drive electric currents through the base of the pan, so the pan itself becomes the heater and the glass top never gets very hot.

Which planet has the most powerful magnetic field in the Solar System, a bubble big enough to swallow the Sun?

Jupiter's magnetic bubble stretches almost to the orbit of Saturn, and if human eyes could see it from Earth it would look five times larger than the full Moon.

MRI scanners build images mainly from signals given off by the nuclei of which element in the body's water and fat?

Hydrogen nuclei are single protons that behave like tiny compass needles, lining up with the scanner's field and giving off a radio signal when a pulse knocks them out of line.

Which animals are thought to imprint on the magnetic signature of their birth coast and return years later to nest?

Sea turtles head out into the open ocean as hatchlings, yet a grown female loggerhead makes the long trip back to her home beach to lay her own eggs.

The first guitar with magnetic pickups, a 1931 lap steel by Rickenbacker, was nicknamed after which piece of cookware?

The Frying Pan got its name from its circular body and long neck, and its pickup arched a pair of horseshoe magnets over the steel strings.

In which everyday device does a coil fixed to a cone shuttle back and forth in a magnet's field to make sound?

Loudspeaker drivers still follow the moving-coil cone that Kellogg and Rice built in 1925: the audio current turns the coil into a magnet that the fixed one pushes and pulls.

Which former bookbinder's apprentice showed in 1831 that moving a magnet near a coil makes an electric current flow?

Michael Faraday had little formal education, yet the effect he first saw with two coils wound on an iron ring is the way the generators in power plants still make electricity.

Which company shipped the first hard disk drive in 1956, a magnetic store that weighed over a ton?

IBM built the drive into its RAMAC computer, and the unit was so bulky that it had to be moved around with forklifts and delivered in large cargo planes.

Which company launched the Compact Cassette in 1963 and later let rivals use the magnetic tape format for free?

Philips engineer Lou Ottens led the team that designed it, and from 1966 the company licensed the patented format to other makers without charge.

Which dark features on the Sun are cooler than their surroundings because strong magnetic fields block rising heat?

Sunspots usually appear in pairs of opposite magnetic polarity, like the two ends of a buried horseshoe magnet, and George Ellery Hale first tied them to magnetism in 1908.

Zebra stripes of reversed magnetism in rocks beside mid-ocean ridges gave geologists the first key test of which idea?

Seafloor spreading turns the ocean crust into a tape recorder: new rock locks in the direction of Earth's field as it forms, so each reversal leaves a matching stripe on both sides of the ridge.

The cavity magnetron, a magnet-wrapped tube that powered wartime radar, now sits inside which kitchen appliance?

Microwave ovens exist because engineer Percy Spencer noticed in 1945 that a radar set was melting the candy bar in his pocket; the first food he cooked on purpose was popcorn.

Which English astronomer sailed the Atlantic on the Paramour and in 1701 published the first chart of compass variation?

Edmond Halley was made a Royal Navy captain for the voyage, and his chart was the first to draw lines through places with the same compass error, lines long known as Halleyan.

A geomagnetic storm in March 1989 tripped the power grid of which Canadian province, leaving it dark for nine hours?

Quebec sits on a vast shield of rock that conducts poorly, so the storm's currents surged along the long power lines instead and the network went down in under 90 seconds.

Which Scottish physicist showed in 1865 that electricity, magnetism and light are all aspects of one thing?

James Clerk Maxwell found that electric and magnetic fields travel through space as waves at the speed of light, which led him to predict the existence of radio waves.

Which French physicist showed in 1820 that parallel wires carrying current attract or repel each other?

André-Marie Ampère found that wires carrying current the same way attract while opposite currents push apart, work that earned him the nickname the Newton of electricity.

By convention, the arrows on field lines drawn around a bar magnet point which way outside the magnet?

North to south is how the lines run through the air, but they have no start or end: each one carries on through the body of the magnet and closes into a loop.

The cheap, brittle, dark ceramic used for most refrigerator magnets and small motor magnets goes by which name?

Ferrite is chemically a close cousin of rust, which is why it costs so little to make and shrugs off corrosion.

The strongest permanent magnets made, found in headphones and wind turbines, are alloys of elements from which group?

Rare earths such as neodymium can be about as abundant in the crust as tin or lead, but their ores do not gather in rich seams, so the name is misleading.

Which laboratory steers protons round a 27-kilometre ring near Geneva using 1,232 magnets of 35 tonnes each?

CERN chills the Large Hadron Collider's magnets to 1.9 kelvin so that they carry current without resistance, making the machine the largest cryogenic facility in the world.

Which crooner's $50,000 order for Ampex recorders in the 1940s let him pre-record his radio show on magnetic tape?

Bing Crosby had stayed off the air for seven months over the right to pre-record, and his order let a six-man firm build the machines behind America's first tape-delayed radio broadcast.

A 2013 study of 70 pets found which animals tend to align with Earth's magnetic field when relieving themselves?

Dogs lined up along the compass axis only while the field was calm, the first time a predictable reaction to its natural swings had been shown in a mammal.

Which machine, found in fans, drills and washing machines, turns current into rotation using coils and magnets?

Electric motors are so common that between them they consume about half of the world's electricity.

The magnetism of a fridge magnet comes mainly from which quantum property of its electrons?

Spin makes every electron a tiny magnet, but in most materials the electrons pair off pointing opposite ways and cancel out, which is why so few substances can hold a field.

Which doughnut-shaped fusion machine, named with a Russian acronym, uses powerful magnets to hold plasma in place?

Tokamak is usually spelled out as the Russian for toroidal chamber with magnetic coils, and it is the leading magnetic design in the race to produce fusion power.

Satellites confirmed in 1958 that Earth's magnetic field traps fast charged particles in which zones?

Van Allen belts are stocked mostly by particles from the solar wind, and they are named after the University of Iowa physicist who described them in 1958.

Roller coasters and high-speed trains can brake without friction when magnets induce what in a moving metal fin?

Eddy currents make the moving metal fight its own motion with no parts to wear out, but the drag fades as the speed drops, so a friction brake must still hold a stopped train.

World War II navies fitted ships with coils that cancelled their magnetism so they would not set off which weapons?

Naval mines sensed how a steel hull concentrates Earth's field, and when coils proved too costly for every ship, crews dragged a live cable up the hull instead: 400 ships in four days before Dunkirk.

The theory that churning liquid metal deep inside Earth generates its magnetic field is named after which machine?

A dynamo turns motion into electricity, and Joseph Larmor proposed in 1919 that a natural one made of flowing, conducting fluid could keep a planet's field going.

The north magnetic pole has drifted out of Arctic Canada and is heading across the Arctic Ocean toward which region?

Siberia has been its heading for decades, and the pace has quickened from about 9 kilometres a year in 1970 to more than 50 a year in the early 2000s.

Ernest Lawrence won a Nobel Prize for which machine that uses a magnet to bend speeding particles into a spiral?

The cyclotron was the first accelerator to send particles round and round, so they cross the same accelerating gap many times and pick up energy on every lap.

Which moon, the largest in the Solar System, is the only one known to generate its own magnetic field?

Ganymede's field is strong enough to give the moon auroras of its own, even though it sits inside the far greater field of its parent planet.

The bar of soft metal laid across the poles of a stored horseshoe magnet to stop it weakening is called what?

A keeper gives the field an easy route from one pole to the other, so the magnet's own stray field cannot slowly undo its magnetism in storage.

Which phenomenon, discovered in 1933, sees a superconductor expel magnetic fields as it is chilled?

The Meissner effect is the work of currents that flow without loss in the skin of the superconductor, creating a field that exactly cancels the outside one within the material.

Compounds of which strongly magnetic metal are injected into patients to make tissue stand out in an MRI scan?

Gadolinium changes character at about room temperature: a cold lump clings to a magnet much as steel does, and warming it past roughly 20 °C makes it let go.

Which phenomenon, found by a student in 1879, is the sideways voltage across a live conductor in a magnetic field?

The Hall effect was first measured 18 years before anyone had discovered the electron, and sensors built on it are now a standard way to detect magnetic fields.

Which medieval scholar wrote the first surviving treatise on magnets in 1269, in the form of a letter to a soldier?

Peter Peregrinus gave the earliest detailed account of a freely pivoting compass needle, the key part of the dry compass that sailors were soon steering by.

Which Dutch physicist won a 1902 Nobel Prize for finding that a magnetic field splits the lines in a spectrum of light?

Pieter Zeeman's split lines move further apart as the field grows, so astronomers use them to map magnetism across the face of the Sun and on other stars.

Which Royal Navy officer led the first party to reach the north magnetic pole, on the Boothia Peninsula in 1831?

James Clark Ross planted the British flag there while serving on his uncle's Arctic expedition, and later led a voyage to find the opposite magnetic pole that put the Ross Sea on the map.

Which physics rule, stated in 1834, explains why a strong magnet dropped down a metal pipe falls in slow motion?

Lenz's law says an induced current always flows so as to oppose the change that created it, so the falling magnet sets up currents in the pipe wall that push back against its fall.

The SI unit of magnetic flux is named after which physicist, a Göttingen professor sacked in 1837 for defying his king?

Wilhelm Weber was one of the Göttingen Seven, professors who refused an oath to the new king of Hanover after he annulled the constitution; two of the others were the Brothers Grimm.

Which storage medium, launched in 1971 at 8 inches across, kept data on a thin plastic disc with a magnetic coating?

The floppy disk began 8 inches wide and shrank to 5¼ and then 3½ inches, the three sizes that became its most popular formats.