50 Fun Facts About Kelvin

The kelvin is the base unit of temperature in which set of units?

It is one of seven SI base units, and the only one whose scale starts at a true physical zero.

What is the symbol for the kelvin?

'Degree Kelvin' with the ° sign was officially dropped in 1967–68.

What do you add to a Celsius temperature to convert it to kelvins?

A one-kelvin step and a one-degree-Celsius step are exactly the same size.

What temperature does 0 K represent?

It is the lowest possible temperature, the point at which classical particle motion would stop.

What was Lord Kelvin's name before he was ennobled?

He was knighted in 1866 and became a baron in 1892.

In which city was the future Lord Kelvin born?

His father taught mathematics there before moving the family to Glasgow in 1833.

At what age did the young Thomson start studying at the University of Glasgow?

Not precocity: the university then provided an elementary education for able boys, and 10 was a normal starting age.

For how many years was Kelvin professor of Natural Philosophy at Glasgow?

He refused offers from world-famous universities and stayed until retiring in 1899.

At which Cambridge college did Thomson study, becoming a fellow in 1845?

He then worked in Regnault's Paris laboratory before taking the Glasgow chair at 22.

Kelvin's title refers to what natural feature near his Glasgow laboratory?

His title was Baron Kelvin of Largs, the Ayrshire town where he built his mansion Netherhall.

In what year did Thomson publish 'On an Absolute Thermometric Scale'?

In a footnote he derived −273 °C for the bottom of the scale from the thermal expansion of gases.

Which physicist worked with Thomson through the 1850s on the formula behind the absolute scale?

He was named after the same man as the SI unit of energy; Thomson's Carnot function turned out to be a constant.

Kelvin's scale was built on the theoretical heat engine of which French engineer?

His idealised reversible cycle links the ratio of heat taken in and rejected to the ratio of absolute temperatures.

In the early 20th century, the Kelvin scale went by which nickname?

People even used the °C symbol for it, just counting from the bottom of the scale.

Which of Kelvin's relatives coined the term 'triple point' in 1873?

At a substance's triple point, solid, liquid and gas coexist at one unique temperature and pressure.

From 1954 to 2019, the kelvin was defined so that the triple point of water was exactly what?

That is 0.01 °C; the triple point was preferred to the melting point because it could be measured ten times more precisely.

What change did the 13th CGPM make to the unit in 1967–68?

Since then the SI convention has been that the kelvin is never written or spoken as a 'degree'.

The 2019 redefinition of the kelvin fixed the exact value of what?

Every 1 K change now corresponds to exactly 1.380649×10⁻²³ joules of thermal energy.

On what date did the 2019 redefinition of the kelvin come into force?

It was the 144th anniversary of the Metre Convention, and the change went almost unnoticed in daily life.

After 2019, where did the measurement uncertainty that used to sit on kB move to?

The triple point of water is now 273.1600(1) K rather than exact.

Which SI derived unit is the only one with a special name derived from the kelvin?

Metric prefixes work too: a millikelvin is a thousandth of a kelvin.

According to SI style rules, how should the unit's name be written in running text?

The symbol K is capitalised because it comes from a person's name, and 283 kelvins is the correct plural.

Which absolute temperature system uses Fahrenheit-sized degrees instead of Celsius-sized ones?

It was proposed in 1859 by another Glasgow professor, W. J. M. Rankine.

Below roughly what colour temperature do black-body light sources look reddish?

Above about 7500 K they look bluish; daylight film wanted about 5600 K.

What effective temperature does the IAU adopt for the Sun's photosphere?

The colour temperature of sunlight above the atmosphere is about 5,900 K.

In photography, what does raising the colour temperature setting do to an image?

Lowering it makes the picture more dominated by reddish, 'warmer' colours.

In electronics, the kelvin is used to express what property of a circuit?

Johnson–Nyquist noise in resistors is thermal noise tied to kB.

The Unicode 'Kelvin sign' (U+212A) exists, but what does the Unicode standard recommend using instead?

The Ohm sign and Angstrom sign are the other two 'letterlike symbols' with the same advice.

0 K corresponds to what temperature in Fahrenheit?

Nothing can be cooled to it, but Bremen physicists reached 38 trillionths of a kelvin above it in 2018.

Who first raised the question of a lowest possible temperature in 1703, while improving the air thermometer?

Extrapolating gas volume to zero later pointed to about −273 °C.

Which element stays liquid at normal pressure even at temperatures near 0 K?

Its atoms' large zero-point motion stops them settling into a solid unless squeezed hard.

For which project was Thomson knighted by Queen Victoria in 1866?

His mirror galvanometer rescued the 1858 cable after the chief electrician's equipment proved too insensitive.

Which instrument, patented by Thomson in 1858, made the weak signals of the Atlantic cable readable?

He also patented the siphon recorder; the board had been unenthusiastic until Whitehouse's gear failed.

On which ship did Thomson sail on the 1865 cable-laying expedition?

He had sailed on the Agamemnon in 1857–58; the Great Eastern finished the job in 1866.

What slogan summed up the 1866 cable's improvement over dispatches by ship?

Queen Victoria and President Buchanan had exchanged the first, painfully slow, messages in 1858.

Kelvin's 1897 estimate for the age of the Earth was how many years?

Radioactive heating, discovered in 1903, was the missing energy source, and radiometric dating overturned him in 1907.

Kelvin's short estimate for Earth's age put him in public dispute with the supporters of which theory?

He clashed with Huxley and Tyndall over whether there had been enough time for gradual evolution.

Which physicist argued in 1904, with Kelvin present, that radioactivity supplied the energy Kelvin's sums lacked?

Kelvin had regarded the earlier announcement of X-rays as a hoax.

Kelvin was the first scientist to be raised to what?

He was ennobled in 1892, partly for thermodynamics and partly for opposing Irish Home Rule.

Where is Lord Kelvin buried?

His grave lies near those of Newton, Herschel and Darwin.

How did Thomson propose to his second wife, Fanny Blandy, in 1874?

He sailed the Lalla Rookh into Madeira and signalled 'Will you marry me?'; she signalled back 'Yes'.

Which navigational instrument did Kelvin work to perfect in the 1880s?

Iron hulls were throwing compasses off, and he designed an adjustable one to correct the deviation.

What is the Kelvin water dropper, invented in 1867?

Two falling streams of drops charge two buckets until a spark jumps; it's nicknamed Lord Kelvin's thunderstorm.

The Kelvin–Helmholtz instability, seen in wave-like clouds, is caused by what?

It shows up in Earth's clouds, the Sun's atmosphere and Jupiter's Red Spot.

At what angle to a boat's path do the arms of the Kelvin wake pattern lie in deep water?

Remarkably, it does not depend on the speed of the boat, only on gravity waves in deep water.

Kelvin extended the second law of thermodynamics to the whole cosmos, originating which idea?

His 1862 'Kelvin's paradox' used the second law to argue the universe could not be infinitely old.

Which honour did Kelvin receive in the 1902 Coronation Honours, as one of its first members?

He was also made a Privy Councillor the same day.

Which Glasgow museum holds a permanent exhibition of Kelvin's papers and instruments, down to his pipe?

He was Chancellor of the university from 1904 until his death in 1907.

Which 18th-century gas law, extrapolated, first suggested a gas would reach zero volume at about −273 °C?

Charles, Dalton and Gay-Lussac found gases shrink by about 1/273 of their volume per degree Celsius.

Which Royal Society honour did Thomson receive in 1883, seven years before becoming its president?

He led the Royal Society from 1890 to 1895 and separately served three terms as president of the Royal Society of Edinburgh.