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"The kelvin, symbol K, is the SI unit of thermodynamic temperature. It is defined by taking the fixed numerical value of the Boltzmann constant k to be 1.380 649 × 10 −23 when expressed in the unit J K −1, which is equal to kg m 2 s −2 K −1, where the kilogram, metre and second are defined in terms of h, c and ∆ν Cs." [1]
Measurement of the spectrum of electromagnetic radiation from an ideal three-dimensional black body can provide an accurate temperature measurement because the frequency of maximum spectral radiance of black-body radiation is directly proportional to the temperature of the black body; this is known as Wien's displacement law and has a ...
The calorie is a unit of energy that originated from the caloric theory of heat. [1] [2] The large calorie, food calorie, dietary calorie, kilocalorie, or kilogram calorie is defined as the amount of heat needed to raise the temperature of one liter of water by one degree Celsius (or one kelvin).
[2] [7] [8] The 2019 revision of the SI now defines the kelvin in terms of energy by setting the Boltzmann constant to exactly 1.380 649 × 10 −23 joules per kelvin; [2] every 1 K change of thermodynamic temperature corresponds to a thermal energy change of exactly 1.380 649 × 10 −23 J.
Calorimetry is measurement of quantity of energy transferred as heat by its effect on the states of interacting bodies, for example, by the amount of ice melted or by change in temperature of a body. [3] In the International System of Units (SI), the unit of measurement for heat, as a form of energy, is the joule (J).
The specific heat capacities of iron, granite, and hydrogen gas are about 449 J⋅kg −1 ⋅K −1, 790 J⋅kg −1 ⋅K −1, and 14300 J⋅kg −1 ⋅K −1, respectively. [4] While the substance is undergoing a phase transition , such as melting or boiling, its specific heat capacity is technically undefined, because the heat goes into ...
The CGS energy unit is the erg and the imperial and US customary unit is the foot pound. Other energy units such as the electronvolt , food calorie or thermodynamic kcal (based on the temperature change of water in a heating process), and BTU are used in specific areas of science and commerce.
kT (also written as k B T) is the product of the Boltzmann constant, k (or k B), and the temperature, T.This product is used in physics as a scale factor for energy values in molecular-scale systems (sometimes it is used as a unit of energy), as the rates and frequencies of many processes and phenomena depend not on their energy alone, but on the ratio of that energy and kT, that is, on E ...