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General Information 11
Temperature
Kelvin (K) The kelvin belongs to a group of seven SI base
units used as a quantitive unit of thermodynamic temperature.
It is named after Lord William Thompson Kelvin, a Scottish
physicist (1824–1907). In 1848 he suggested a scale of temperature,
now called kelvin, in which the zero point is absolute
zero – the temperature at which the motions of particles
cease and their energies become zero. The units of kelvin
and degree celsius temperature intervals are identical (thus
1ºC 1 K), but the point of absolute zero in celsius is minus
273.15 K, thus 0ºC 273.15 K.
It is now customary for temperature and temperature intervals
to be described in degrees celsius (ºC) although colour temperature
of light sources is measured in degrees kelvin (K).
Celsius (ºC) The celsius scale is a scale of temperature on
which water freezes at 0º and boils at 100º under standard
conditions. It was devised by Anders Celsius, a Swedish
astronomer (1701–44). He originally designated zero as the
boiling point of water and 100º as freezing point. The scale
was later reversed.
Centigrade A temperature scale using the freezing point of
water as zero and the boiling point of water as 100º. The scale
is now officially called celsius (see above) to avoid confusion in
Europe where the word can mean a measure of plane angle
and equals 1/10 000 part of a right angle.
Fahrenheit (ºF) A scale of temperature still used in the USA
which gives the freezing point of water as 32º and boiling
point as 212º. Named after Gabriel Daniel Fahrenheit, a
Prussian physicist (1686–1736) who invented the mercurial
barometer. The Fahrenheit scale is related to the Celsius scale
by the following relationships:
temperature ºF (temperature ºC 1.8) 32
temperature ºC (temperature ºF 32) 1.8
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