50 Fun Facts About Electricity and Magnetism

Luigi Galvani's 1780s discovery of "animal electricity" came when sparks made the severed legs of which animals twitch?

Frogs twitching on his bench convinced Galvani that animals run on electricity, and talk of such "galvanism" helped inspire Mary Shelley's Frankenstein.

The word "electricity" comes from the Greek name for which material, which attracts light objects after being rubbed?

Amber is "elektron" in Greek, and people around the ancient Mediterranean knew that a rod of it rubbed with cat's fur would pull in feathers.

Which 18th-century experimenter borrowed a military term to call his linked set of electrical capacitors a "battery"?

Benjamin Franklin took the word in 1749 from the military term for weapons working together, and later proposed flying a kite in a storm to show that lightning is electrical.

In the War of the Currents, Thomas Edison campaigned against which electrical system promoted by George Westinghouse?

Alternating current was painted as deadly by Edison's allies, who killed stray dogs with it at public demonstrations, yet it became the standard for power grids.

Which layer of Earth, a churning mix of molten iron and nickel, generates the global magnetic field?

The outer core is stirred by heat escaping from the planet's centre, and the field inside it is about 50 times stronger than the one felt at the surface.

Rubbing a balloon on your hair leaves the balloon negatively charged because it has picked up extra what?

Electrons move from the hair to the balloon, leaving every strand positively charged, which is why the hairs push apart and stand on end.

Which precious metal is the best electrical conductor of all, narrowly beating the copper used in household wiring?

Silver conducts electricity better than any other metal, but its high cost means it is rarely used for that, leaving copper to wire the world.

Old-style Christmas tree lights all went dark when a single bulb failed because they were wired in which arrangement?

A series circuit gives the current only one path, so a single dead bulb breaks the whole loop until the faulty one is found and replaced.

Which device lets a scrapyard crane lift a load of scrap steel and then release it at the flick of a switch?

An electromagnet is magnetic only while current flows through its coil; the first one, built in 1824, weighed seven ounces yet lifted nine pounds.

Which Art Deco skyscraper, for decades the world's tallest, is struck by lightning about two dozen times a year?

The Empire State Building is topped with a lightning rod, and tall grounded structures like it concentrate the electric field beneath a thundercloud.

Which English former bookbinder's apprentice, largely self-taught, discovered electromagnetic induction in 1831?

Michael Faraday wrapped two coils of wire around an iron ring and found that starting a current in one made a momentary current flow in the other.

Which naturally magnetised rock was suspended so it could turn, making the first magnetic compasses for navigators?

Lodestone means "leading stone" in Middle English, and it is one of only a very few minerals found naturally magnetised.

Which sky display, seen mostly near the poles, is caused by charged particles from the Sun striking the atmosphere?

The aurora takes its name from the Roman goddess of dawn, and Earth's magnetic field is what steers the incoming particles towards the polar regions.

Which planet's magnetic field is the most powerful in the Solar System, with a tail reaching almost to Saturn's orbit?

Jupiter has a magnetic field about 20 times stronger than Earth's, and if its magnetosphere were visible it would look five times wider than the full Moon.

Which metal, the least dense of all, is used in the rechargeable batteries honoured by a 2019 Nobel Prize?

Lithium is light enough to float on water, and the batteries built around it made mobile phones, laptops and electric cars practical.

Which safety device protects a circuit with a thin wire designed to melt when too much current flows?

A fuse is a sacrificial device that must be replaced once its wire has melted, one reason circuit breakers have taken its place in many settings.

Sprinkling which powder on a sheet of paper laid over a bar magnet reveals the curved lines of its magnetic field?

Iron filings line up along the direction of the field, but the neat gaps between their lines are made by the filings themselves, because the real field is continuous.

Which American portrait painter turned inventor opened a telegraph line in 1844 with the words "What hath God wrought"?

Samuel Morse had already made his name painting portraits when, in middle age, he helped develop a telegraph that needed only a single wire.

Which office machine, born of Chester Carlson's 1930s kitchen experiments, uses static charge to stick toner to paper?

The photocopier uses xerography, a dry process devised by a patent attorney who found copying documents by hand painful and tedious.

Which eerie blue glow on ships' masts during thunderstorms did sailors sometimes welcome as a good omen?

St. Elmo's fire, named after the patron saint of sailors, is plasma that forms when a strong electric field makes the air glow around a pointed object.

Which Scottish physicist's equations of the 1860s showed that light is a wave of electric and magnetic fields?

James Clerk Maxwell also predicted radio waves from the same theory, and separately worked out that Saturn's rings must be made of numerous small particles.

Which inventor, namesake of the SI unit of magnetic flux density, quit Thomas Edison's company after only six months?

Nikola Tesla left the Edison Machine Works to strike out on his own, and his work had slipped into relative obscurity before the unit was named in his honour in 1960.

Which unit of energy, equal to 3.6 million joules, do electricity companies use to bill household customers?

A kilowatt-hour is the energy a one-kilowatt appliance uses in an hour, and a typical home gets through a few hundred to a few thousand of them a month.

What name is given to materials such as glass, rubber and most plastics that do not let electric current flow freely?

Insulators such as glass and paper have very high resistivity, which is why the wires inside a cable are wrapped in plastic instead of being left bare.

Which device changes the voltage of mains electricity, stepping it down between power lines and household sockets?

A transformer works by induction: a varying current in one coil creates a changing magnetic flux, which induces a voltage in a second coil wound alongside it.

Which machine inside fans, drills and washing machines uses magnetic fields to turn electrical energy into rotation?

A motor can also run in reverse: electric cars spin theirs while braking to recover energy that would otherwise be lost as heat and friction.

Which machine, a favourite of science classrooms, uses a moving belt to build up charge on a hollow metal terminal?

The Van de Graaff generator began in 1929 as a tin can and a silk ribbon, and an inexpensive tabletop version can still produce around 100,000 volts.

Passing an electric current through water, first done with a battery in 1800, splits it into oxygen and which gas?

Hydrogen bubbles off in twice the amount of the oxygen, matching the two-to-one ratio in water's formula, H2O.

The ampullae of Lorenzini, jelly-filled pores that sense the electric fields of prey, are found on which predators?

Sharks have the pores clustered around the snout and mouth, where they pick up the weak electrical signals given off by a prey animal's muscle contractions.

The magnetic compass was first made as a fortune-telling device about 2,000 years ago in which country?

China used the compass for divination from the Han dynasty and only turned it to navigation in the 11th century, more than a thousand years later.

Which scientist, first to produce aluminium metal, showed in 1820 that an electric current deflects a compass needle?

Hans Christian Ørsted gave the first proof that electricity and magnetism are linked, and the discovery won him the Royal Society's Copley Medal the same year.

Which German schoolteacher's law states that the current through a conductor is proportional to the voltage across it?

Georg Ohm found the rule with equipment he had built himself while working as a school teacher, and the unit of electrical resistance now carries his name.

Which SI unit of electric current is named after a French physicist who laid the foundations of electrodynamics?

The ampere honours André-Marie Ampère, and a current of one ampere means one coulomb of charge flowing past a given point every second.

Mains electricity in large parts of the world completes 50 cycles every second, a frequency measured in which unit?

Hertz is the unit, and the Americas typically run at 60 rather than 50; it honours the first person to give conclusive proof that electromagnetic waves exist.

Which metal, named after the "goblin ore" of German miners, joins iron and nickel as a common ferromagnetic element?

Cobalt was extracted from those troublesome ores around 1735, which made it the first new metal to be discovered since ancient times.

Which rare-earth element gives its name to the strongest permanent magnets sold commercially, first developed in 1984?

Neodymium magnets were developed independently by an American carmaker and a Japanese metals firm in the same year, and now sit inside hard disk drives and cordless tools.

Which hospital scan, performed inside a superconducting magnet cooled by liquid helium, uses no ionising radiation?

MRI builds its pictures from strong magnetic fields and radio waves instead of X-rays, which sets it apart from both CT and PET.

Which planet lost its magnetic field about four billion years ago, letting the solar wind thin out its atmosphere?

Mars still has patches of magnetised crust, a fossil record of the field it lost, which may have been knocked out by numerous asteroid strikes.

Which waterfall powered the Adams Power Plant of 1895, whose machinery was supplied by George Westinghouse's company?

Niagara Falls fed the first large-scale power plant of its kind in the world, and just one building from the original complex still stands, now a National Historic Landmark.

Despite its name, the electric eel, which can deliver shocks of up to 860 volts, belongs to which group of fishes?

Knifefish from South America are its true relatives, and when Linnaeus described the animal in 1766 he placed it in the same genus as the banded knifefish.

Which physician to Queen Elizabeth I argued in his 1600 book De Magnete that Earth is itself a giant magnet?

William Gilbert reached the idea by experimenting on a small model Earth he called the terrella, and he was the first person to argue that the planet's centre is iron.

Which physicist, a 1903 Nobel winner alongside his wife, names the temperature at which magnets lose their magnetism?

Pierre Curie showed that magnetism is lost at a critical temperature, which for iron is about 770 °C.

Which glass container of the 1740s, the original form of the capacitor, stored charge from static electricity machines?

The Leyden jar, named after the Dutch university city of Leiden, was discovered independently by a German cleric and a Dutch scientist within months of each other.

Superconductivity was discovered in 1911 when which metal, cooled with liquid helium, abruptly lost all resistance?

Mercury lost its resistance at 4.2 kelvin, but the exact date of the discovery was pinned down only a century later, when the experimenter's notebook was found.

Volta's pile of 1800, the first true battery, stacked brine-soaked cardboard between discs of copper and which metal?

Zinc and copper pairs made the first battery that could supply a continuous current, and the extra discs Volta put at each end of the stack later proved unnecessary.

Which massless particle, given its modern name in 1926, acts as the carrier of the electromagnetic force?

The photon is the quantum of the electromagnetic field, which makes it the particle of light and radio waves as well as the carrier of the force.

Thomas Edison's Pearl Street Station, his first commercial power plant in America, opened in 1882 in which city?

New York got the plant in Manhattan's Financial District, where it burned coal and began by lighting 400 lamps for just 82 customers.

Stripes of reversed magnetism in seafloor rock, mirrored either side of mid-ocean ridges, helped confirm which theory?

Plate tectonics passed its first key test in 1963, when the stripes were read as new crust recording each reversal of Earth's magnetic field as it spread from the ridges.

Induction hobs heat pans with a rapidly changing magnetic field, so they typically need cookware made of which material?

Cast iron works because the hob's field can drive a concentrated current through it, heating the pan itself, while copper and aluminium pans typically stay cold.

Which metal, with the highest melting point of any, forms the glowing filament of a traditional incandescent light bulb?

Tungsten melts only at 3,422 °C, and it also has the lowest vapour pressure and the highest tensile strength of any pure metal.