History of Science

Kelvin scale: no degrees below zero

Temperature scale named after Lord Kelvin

We see the name of the Swedish astronomer Anders Celsius (1707-1744) every day in the weather report. The Americans are equally familiar with Daniel Gabriel Fahrenheit (1686-1736), who also invented the mercury thermometer. In parts of Italy and Switzerland, cheese makers still use a dish that René Antoine Ferchault de Réaumur drew up in 1731.

Lord Kelvin (1824-1907) is less common in daily life, although his temperature scale is very common in science. He was born William Thomson, and when he was rewarded in 1892 for being a scientific with a baron title, he took the name of the Kelvin River, which flowed alongside his laboratory at the University of Glasgow.

Kelvin dish had to be practical

The scale is based on the work of Celsius, because 1 degree Kelvin (K) is equal to 1 degree Celsius. But the starting point is different. In 1848 Lord Kelvin wrote a famous treatise in which he stated that degrees below zero were not practical.

He therefore proposed not to place the zero point on the freezing point of water - the zero point should be the absolute zero point, the lowest possible temperature, at which all molecular activity stops. This point is at -273.15 degrees Celsius. According to the Kelvin scale, water freezes at 273.15 K and boils at 373.15 K.

The Kelvin scale is used, for example, to express color temperatures. This is the temperature that a black body must have to emit light of a certain color. The color temperature of the sunlight at sunrise is around 1800 K, that of powerful sunlight 6000 K, while a heavily cloudy sky has a value of 10,000 K.

Video: Absolute Zero: Absolute Awesome (December 2019).

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