Kelvin scale of temperature

Temperature is our sensory feeling of how hot or cold a substance is. In thermodynamics, temperature is a measure of the average energy of the motions of matter's particle constituents (atoms and molecules). The zero point of the Kelvin scale is the temperature where there is no heat in a molecule. Kelvin scale is also called the ‘absolute scale of temperature’

Background: Kelvin [K] represents kinetic energy. 1 kelvin [K] = 1.38064878066852E^-23 joule. Kelvin scale was built up with no reference to a cold or hot object. It focuses only on the energy in a molecule and thus it became the thermodynamic scale of temperature. The kelvin is the base unit of temperature in the International System of Units (SI), abbreviated as "K". The Kelvin unit directly links itself with energy through the Boltzmann constant.

The idea for the Kelvin scale came from a discovery in the 1800s of a relationship between the volume and the temperature of a gas. Scientists theorized and proved that the volume of gas becomes zero at a temperature of minus -273.16 degc. This temperature is called absolute zero because the atoms cease to carry any energy at -273.15 deg. This became the lower end of Kelvin's scale.

Fahrenheit and Celsius scale of temperatures represent ‘coldness’ and ‘hotness’ perception of a substance. They do not symbolize energy. 0 deg Celsius is not 0 energy. Therefore, Fahrenheit and Celsius are not used in thermodynamics. In thermodynamics, the temperature is kinetic energy.

Kelvin[T] links Kinetic energy by Boltzmann equation, Average KE = KB x T

Boltzmann constant: KB is called the Boltzmann constant. The Boltzmann constant (kB or k) is the proportionality factor that relates the average relative thermal energy of particles in a gas with the thermodynamic temperature of the gas. The Boltzmann constant is defined to be exactly 1.380649×10^?23 joules per kelvin. Boltzmann constant is a fixed number. It does not depend on how low or how high the temperature is.

As part of the 2019 redefinition of SI base units, the Boltzmann constant is one of the seven "defining constants" that have been given exact definitions. They are used in various combinations to define the seven SI base units.

Discovery of Kelvin scale: The idea for the Kelvin scale came by a discovery in the 1800s of a relationship between the volume and the temperature of a gas. Scientists found that the volume of gas becomes zero at a temperature of minus -273.16 degc,

Image credit: Google

Charles’s law plots of temperature and volume and temperature and pressure are shown above. A remarkable feature of these plots is that if the straight line is extrapolated down to a value of zero volume, the corresponding temperature (the intercept on the temperature axis) is -273.15 degrees Celsius. On the right-side plot when pressure vs. temperature data is extrapolated to a pressure of zero, it intercepts the temperature axis at exactly -273.15 degrees Celsius. This observation led to believe that at – 273.15 degc is the lowest possible temperature when the kinetic energy ceases to exist in a substance. This is how – 273.15 degc became the lower end of the Kelvin scale of temperature. At -273.15 degc the thermal molecular motion of the gas molecules nearly ceases. Kelvin added 273.15 degc to the Celsius scale and converted the Celsius scale to the Kelvin scale keeping the incremental increase of temperature the same in the Kelvin scale, 1 deg Celsius = 1 Kelvin.

Kelvin [K]= Actual temperature in Celsius + 273.5 Celsius.

Kelvin scale is an absolute scale of temperature

The best way to understand why the Kelvin scale is referred to as the absolute scale of temperature is to compare it to the absolute pressure scale. The pressure of the atmosphere is latent on a pressure gauze; what we observe is the gauze pressure. Absolute pressure is the total pressure that results from adding atmospheric pressure to gauze pressure.

The temperature is represented in the Celsius temperature scale on a thermometer in the same way. The temperature-related energy is still latent. The absolute energy scale, which accounts for all of the kinetic energy for each degree of Celsius, is created when we add 273.15 degrees Celsius.

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