Charles's law

Charles's law (also known as the law of volumes) is an experimental gas law that describes how gases tend to expand when heated. A modern statement of Charles's law is:

When the pressure on a sample of a dry gas is held constant, the Kelvin temperature and the volume will be in direct proportion.

This relationship of direct proportion can be written as:

V\propto T

So this means:

{\frac {V}{T}}=k,\quad {\text{or}}\quad V=kT

where:

$V$ is the volume of the gas,
$T$ is the temperature of the gas (measured in kelvins), and
$k$ is a constant for a particular pressure and amount of gas.

This law describes how a gas expands as the temperature increases; conversely, a decrease in temperature will lead to a decrease in volume. For comparing the same substance under two different sets of conditions, the law can be written as:

${\frac {V_{1}}{T_{1}}}={\frac {V_{2}}{T_{2}}}$

The equation shows that, as absolute temperature increases, the volume of the gas also increases in proportion.