50 Fun Facts About Magnets

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

Lodestones were found there, in Anatolia; the site is Manisa in modern Turkey. Suspended lodestones became the first compasses.

Lodestones are naturally magnetised pieces of which mineral?

Only a small fraction of that mineral on Earth is found magnetised, and the name lodestone means course stone or leading stone in Middle English.

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

Everything else responds to a magnetic field too, but so weakly that the effect usually needs lab instruments to detect.

What happens if you break a bar magnet in two to try to separate its poles?

Poles are just a way of naming the two ends. No one has ever isolated a single magnetic pole, or monopole, though physicists keep looking.

Heating a magnet past what threshold destroys the alignment of its domains and demagnetises it?

Molecular motion scrambles the alignment of the magnetic domains, and the magnet loses its field entirely.

That critical demagnetisation temperature is named after which scientist?

Above that point ordered ferromagnetic moments become disordered and the material behaves paramagnetically instead.

In which Chinese dynasty was the magnetic compass first invented, as a divination tool?

It was adopted for navigation by the Song Chinese in the 11th century; Western Europe's first recorded compass use came around 1190.

Which Song dynasty writer described the first navigational compasses in China by 1088?

Those compasses used iron needles magnetised by striking them with a lodestone. Dry compasses appeared in Europe around 1300.

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

North is 0 degrees and the angles increase clockwise, so south is 180 and west is 270. These numbers give bearings and azimuths.

Which British scientist invented the electromagnet in 1824?

His first was a varnished horseshoe of iron wrapped in 18 turns of bare copper wire. Weighing seven ounces, it could lift nine pounds.

What is the main advantage of an electromagnet over a permanent magnet?

The trade-off is that it needs a continuous current to keep its field. Scrapyards use them to pick up and drop heavy iron.

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

The same year, Andre-Marie Ampere showed that iron could be magnetised by placing it inside a current-carrying solenoid.

The tale that Orsted found the electricity-magnetism link by accident in a lecture is what?

He had been hunting for the connection since 1818 and was confused by his results. He also discovered the element aluminium.

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

He experimented with a small model Earth. Before him, some believed Polaris or a magnetic island pulled the compass north.

William Gilbert was personal physician to which English monarch from 1601?

James VI and I renewed the appointment. Gilbert also coined the Neo-Latin word electricus, meaning like amber, the root of electricity.

Gilbert called his spherical model Earth, used to study magnetism, what?

From those experiments he concluded that compasses point north because the whole planet is magnetic, not because of the pole star.

Neodymium magnets were developed independently in 1984 by Sumitomo and which carmaker?

The research was driven by the high cost of samarium-based magnets. GM spun off Magnequench in 1986 to commercialise its version.

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

The compound Nd2Fe14B forms a tetragonal crystal structure. Each Toyota Prius motor needs about a kilogram of neodymium.

Alnico magnets take their name from aluminium, nickel and which other metal?

Until rare-earth magnets arrived in the 1970s, alnico was the strongest permanent magnet type. T. Mishima in Japan began its development in 1931.

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

It nearly doubles the field on the fridge side and leaves almost none on the other, which is why the back of a fridge magnet barely sticks.

The first rigid refrigerator magnets were created in which decade?

They were cylinders or blocks of ferrite with decorations glued on. The flexible sheet version, usually barium ferrite in plastic, came later.

Earth's magnetic field comes from convection of molten metal in which layer of the planet?

Heat escaping the core drives the churning, a natural process called a geodynamo. Surface field strength is 25,000 to 65,000 nanotesla.

Earth's magnetic dipole is tilted roughly how far from the rotational axis?

Picture a giant bar magnet slanted through the planet. The poles also wander slowly, and at irregular intervals the whole field flips.

Magnetically speaking, what is the north magnetic pole, the spot where compass needles point?

Opposite ends attract, so the north end of a compass needle points toward what is magnetically the opposite kind of end.

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

The flips are recorded as stripes in sea-floor rocks spreading from mid-ocean ridges, which also let geologists track continental drift.

The study of Earth's past magnetic field is called what?

Igneous rocks lock in the field's polarity as they cool, so the record of reversals doubles as a dating tool for rocks and sediments.

The SI unit of magnetic flux density, the tesla, was announced in which year?

It honours Nikola Tesla and was proposed by Slovenian engineer France Avcin. One tesla equals one weber per square metre.

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.

Most clinical MRI scanners operate at what magnetic field strength?

Commercial systems range from 0.2 to 7 tesla, and 3-tesla machines are preferred for soft tissue. Research scanners reach 11.7 tesla.

Who proposed in 1973 using a magnetic field gradient for a 2D NMR scan, calling it zeugmatography?

He demonstrated it on two tubes of water at Stony Brook. Mansfield later helped develop echo-planar imaging in Nottingham.

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

It sits in an insulated cryostat, often jacketed with much cheaper liquid nitrogen at 77 kelvin to slow the boil-off.

The superconducting wire in most current magnets is made from niobium and which metal?

It superconducts below 10 kelvin and handles fields up to about 15 tesla. Costlier niobium-tin copes with 25 to 30 tesla.

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

The L0 Series is the test vehicle for the Chuo Shinkansen between Tokyo and Nagoya, whose opening has slipped to no earlier than 2036.

The Shanghai maglev, fastest operational passenger train from 2002 to 2021, uses whose technology?

The Transrapid line covers 30.5 km from Pudong airport in about seven minutes twenty seconds at its historic top speed of 431 km/h.

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

It ran 600 metres between the airport and the railway station at up to 42 km/h, and closed in 1995 because of reliability problems.

As of 2024, how many operational maglev trains existed after a century of development?

Four were in China, one in Japan and one in South Korea. Two more inter-city lines were under construction in Japan and Hunan.

Who showed in 1931 that if magnetic monopoles exist, electric charge must be quantised?

Charge is indeed quantised, which is consistent with monopoles but does not prove them. Candidate detections in 1975 and 1982 proved inconclusive.

A magnetar is an extremely magnetic type of which object?

Their fields reach a billion to a hundred billion tesla, and a tablespoon of magnetar material would weigh over 100 million tons.

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?

The proposed quantum radical pair mechanism is so sensitive that weak radio-frequency noise can disrupt it.

Magnetotactic bacteria line up with Earth's field thanks to internal particles called what?

The iron-rich magnetite grains align the cells passively, like a compass needle, so the bacteria are not really sensing the field at all.

Which couple showed in 1972 that migratory birds respond to the dip of the magnetic field?

Until late in the 20th century, evidence for animal magnetic compasses was almost entirely behavioural, with no known mechanism.

Auroras are caused by charged particles from the Sun colliding with what?

The collisions excite gases, which glow green, red and purple. The lights are steered toward the poles by Earth's magnetic field.

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

Pierre Gassendi, who had read those writings, used the term in 1649 to describe a display seen across France. It entered English in 1828.

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

It emits at 557.7 nanometres at lower altitudes; the rarer red at 630 nanometres appears higher up during intense solar activity.

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

He lived from about 625 to 545 BCE. An ancient Indian medical text describes using magnetite to pull out embedded arrows.

Which Roman author wrote about lodestones and their pull on iron in his Naturalis Historia?

That was the 1st century AD. The earliest surviving descriptions of magnets come from Anatolia, India and China about 2,500 years ago.

The most magnetic natural mineral, with formula Fe3O4, is an oxide of which element?

Apart from extremely rare native iron, it is the most magnetic naturally occurring mineral on Earth, with a Mohs hardness of 5 to 6.

Weakly magnetic substances show paramagnetism, antiferromagnetism and which third type?

These forces are so faint they usually need lab instruments to detect. Ferromagnetism and ferrimagnetism are the strong, everyday kinds.

Whether a steel plate stays magnetised after a magnet is removed depends on its what?

That resistance to demagnetisation varies with the steel's composition and heat treatment. Soft iron magnetises easily but does not stay that way.