## Kelvin and Celsius Scales

Scientists commonly use two temperature scales - the Kelvin and Celsius scales. These temperature scales are closely related. The Celsius scale has been in use longer, and is based on the properties of water.
$0^{\circ} \: Celsius$
is defined to be the freezing point of water at standard pressure
$p_0=1.1325 \times 10^5 N/m^2$

$100^{\circ} \: Celsius$
is defined to be the boiling point of water at standard pressure
$p_0=1.1325 \times 10^5 N/m^2$

The Kelvin scale is more fundamental. An increase of
$1^{\circ} Celsius$
is the same increase as an increase of
$1^{\circ} Kelvin$
, but the zero of the Kelvin scale is defined as the temperature at which no more energy can be extracted from a system, and is equal to
$-273.16^{\circ} Celsius$
.
When doing calculations, typically we use the Kelvin scale eg when using the ideal gas equation of state
$1 pV=nRT$
.