kelvin (K) kelvin (#) Fr.: kelvin The → SI unit of → thermodynamic temperature; symbol K. 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 m2 s-2 K-1 , where the kilogram, meter and second are defined in terms of → Planck's constant (h), → velocity of light (c), and ΔνCs. Named after the Scottish physicist William Thomson, also known as Lord Kelvin (1824-1907), one of the most influential scientists of the 19th century. |