Kelvin Temperature Scale
The Kelvin temperature scale is based upon the kelvin, a unit of thermodynamic temperature, that is defined as the fraction 1/273.16 of the thermodynamic temperature of the triple point of water. The triple point is the temperature at which all three phases of water, solid, liquid, and gas, can coexist. The kelvin temperature scale is named after Scottish physicist William Thomson Kelvin who first described an absolute temperature scale based upon the thermodynamic defintions of absolute zero. The kelvin and the degree Celsius are both units of the International Temperature Scale of 1990 (ITS-90) adopted by the International Committee for Weights and Measures and the General Conference on Weights and Measures (CGPM, Conférence Générale des Poids et Mesures). When referring to the Kelvin temperature scale, the kelvin (symbol K) should be used instead of the term "degree Kelvin" (°K).
The Kelvin temperature scale is an absolute temperature scale used in scientific research. It is the official unit of measurement for temperature according to the Syst(me Internationale of units, or SI units. The Kelvin scale is also known as the thermodynamic scale. According to the Kelvin temperature scale the temperature 0K represents the lowest possible temperature, called absolute zero. Accordingly, the Kelvin scale is an absolute temperature scale.
By using the thermodynamic temperature of the triple point of water and assigning it the temperature of 273.16K, the difference from this temperature becomes the Celsius temperature of a body or substance. Accordingly, the thermal unit on the Kelvin temperature scale is identical to the thermal value of a unit on the Celsius temperature scale. Although the Kelvin temperature scale is one of four major temperature scales (the other major scales include the Celsius, Rakin, and Fahrenheit scales), the Kelvin scale is the most widely used and internationally accepted scale utilized by physicists.
Temperature is not direct measure of the heat energy of a material. Temperature is independent of the amount of material present, whereas the heat energy of an object does depend on the mass of the object.
Although temperature is not a measurement of the amount of heat energy in a substance, it is related to the kinetic energy of the substance. Temperature is proportional to the average kinetic energy of the molecules in an object. The heating of an object reflects a gain in molecular kinetic energy. As their motion increases, so does the number of collisions the molecules make with each other. These collisions cause the kinetic energy to be transformed into heat energy. The more energetic the molecules, the more energetic their collisions become, and the greater the temperature of the object.
As the kinetic energy of the molecules in a substance decreases, the temperature of the substance decreases as well. As the molecules slow down they do not completely stop. As their kinetic energy approaches zero, the temperature of the substance also approaches a lower limit. This limit is called absolute zero, or 0K (-273.15°C and -459.67°F). This small amount of kinetic energy is called the zero-point energy.
Although it is theoretically impossible to experimentally reach absolute zero, scientists have come increasingly close to this value in laboratory experiments. Such extremely cold temperatures can be reached using techniques involving large magnetic fields. Researchers at the University of Colorado, the Massachusetts Institute of Technology, and Stanford University have lowered the temperature of atoms to within a millionth of a kelvin of absolute zero.
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