Kelvin
Abbreviation/Symbol:
K
Worldwide use:
Kelvin is used worldwide, particularly in science. It is part of the International System of Units (SI) and is the fundamental unit for measuring temperature.
Kelvin is often used with other SI units, such as the Pascal for pressure and the Joule for energy.
Definition:
Kelvin is based on the Celsius scale, with the same interval for each degree. However, the start of the Kelvin scale is at absolute zero which is -273.15 degrees C. Kelvin is useful in physics, chemistry, and cosmology.
An advantage of using Kelvin is that there are no negative temperatures. This makes temperature differentials and calculations easier.
Origin:
The Kelvin scale was named after the Scottish physicist William Thomson (lord Kelvin) who made significant contributions to thermodynamics and the study of heat and energy.
Lord Kelvin's work on absolute zero led to the development of this scale. It is based on the idea that temperature is directly proportional to the average kinetic energy of the particles in a substance. Absolute zero is the point where the substance has no kinetic energy and all molecular motion ceases.
The Kelvin scale is almost exclusively used in science and engineering, particularly in fields such as physics, chemistry, and thermodynamics.
Common references:
Absolute Zero, 0K
Melting point of ice, 273.15K
Warm summer's day in a temperate climate, 295K
Normal human body temperature, 310K
Boiling point of water at 1 atmosphere, 373.15K
Usage context:
Kelvin is a unit of measurement used in thermodynamics and temperature.
The Kelvin is almost exclusively used in scientific and engineering contexts such as physics, chemistry and cosmology.
Why can't you get a negative Kelvin value?:
Kelvin is an absolute measurement of temperature meaning it starts at absolute zero, the lowest possible temperature in our universe. Absolute zero is 0 Kelvin(K) or -273.15 degrees Celsius(°C). The Kelvin scale is based on the average kinetic energy of particles in a substance.
You cannot have a negative Kelvin value because at 0K there is no kinetic energy in the particles and are at their lowest possible state of motion. It is impossible for a system to have less energy than zero.
Negative Kelvin would imply that a system has a negative thermal energy which breaks the principles of thermodynamics. It is important to remember that negative temperatures exist in other temperature scales such as the Celsius and Fahrenheit.
Why is Kelvin quoted as K and not °K?:
This abbreviation of K is based on the fact that Kelvin is an absolute temperature scale where zero Kelvin (0K) is absolute zero. Celsius and Fahrenheit which have arbitrary zero points based on freezing and boiling points of water are relative and have degrees of relation whereas the Kelvin scale is based on the absolute thermodynamic temperature.
By omitting the degree symbol, it reminds us that Kelvin is not a relative measurement but a unit of measurement on its own. The use of "K" instead of "°K" for Kelvin was decided as an SI convention to reserve the degree symbol for relative temperature scales.
What happens at absolute zero (0K)?:
At absolute zero, 0 Kelvin (0K) or -273.15 degrees Celsius, the temperature is at the lowest possible point anything can possibly be. At this temperature the kinetic energy of atoms and molecules is zero causing them to come to a complete standstill. All molecular motion ceases and matter becomes still.
Several amazing phenomena occur here. As there is no molecular motion there is no heat energy and this has significant implications for the physical properties of the substance. For example, materials become very brittle and their electrical resistance becomes zero. Gases and liquids freeze into solids.
Scientists have never cooled anything down to absolute zero. However they have been able to see the effects of approaching absolute zero. This has provided insights into the behavior of matter and have led to the understanding of superconductors and Bose-Einstein condensates.