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The Celsius scale is based on 00
for the freezing point of water and 1000 for the
boiling point. Between these defined points, the scale is
divided into 100 equal parts. Other important temperatures on
the Celsius scale include 370 (optimum body
temperature) and 200 (room temperature).
Temperatures below the freezing point of water are affixed
negative values.
The Swedish astronomer Anders Celsius
originally invented the Celsius scale in 1742. It was later
improved upon and given its official name in 1948 by the ninth
General Conference of Weights and Measures. |
Anders Celsius |
The Fahrenheit scale:
This scale is based on 320 for the freezing point
of water and 2120 for its boiling point, the interval
between the two being divided into 180 equal parts.
Daniel Gabriel Fahrenheit, an eighteenth
century German physicist, developed this scale. He determined three
fixed temperatures: 00F for the freezing point of a
mixture of ice, water and salt, 320F for the freezing
point of pure water and 2120F for the boiling point of
pure water. These three values, from lowest to highest, are equal to
–180, 00 and 1000 on the Celsius
scale. He selected the value of 900 for normal body
temperature, which was later revised to 960, but the
final scale required an adjustment to 98.60F.
Sometimes it is necessary to compare a
Celsius temperature to a Fahrenheit temperature. The following
formula can be used to convert a temperature from its representation
on the Fahrenheit (0F) scale to the Celsius (0C)
value: 0C= 5/9 (0F – 32).
The conversion formula for a temperature
that is expressed on the Celsius scale to its Fahrenheit
representation is 0F= 9/5 X 0C.
Absolute temperature scale:
Absolute zero
Absolute zero is that theoretical temperature at which atoms and
molecules of a substance making up a thermodynamic system have the
least possible energy. It is the lowest attainable temperature and
corresponds to –273.15ºC, or –459.67ºF.
The value of Absolute zero was assigned on
the basis of observations of the relationship between the pressure
and temperature of a gas. It was noted that gases confined in a
fixed volume seemed to contract in direct proportion as the
temperature was lowered – as though it would attain zero volume at
what is now called the absolute zero of temperature. Any real gas
however, actually condenses to a solid or liquid at some temperature
higher than absolute zero; therefore the ideal gas law is
only an approximation to real gas behavior.
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A temperature scale that has absolute
zero for its zero point is called an absolute temperature
scale. By international agreement, the Kelvin scale
is used as a standard for this type and is the basis for
all types of scientific temperature measurements. Its unit,
the kelvin (denoted by K, without a degree sign) is defined as
1/273.16 of the triple point of pure water, i.e. the
temperature at which the solid, liquid and gaseous forms of
the substance coexist at equilibrium.
The Kelvin scale is related to the
Celsius scale. A Kelvin temperature is obtained by adding
273.15 to a corresponding Celsius temperature. |
Lord Kelvin |
An absolute temperature scale related to
the Fahrenheit scale is called the Rankine scale. The basic
unit of this scale, the degree Rankine (ºR), is 5/9 of the kelvin.
This scale is used in the United States primarily for engineering
applications.
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