The statement that the volume of a fixed amount of gas varies directly with the temperature of the gas is known as Charles's Law.

Formal statement of Charles's Law:

At constant pressure, the volume of a given mass of an ideal gas is directly proportional to its absolute temperature.

Mathematical expression:

V/T = constant

where:

* V = volume of the gas

* T = absolute temperature of the gas (in Kelvin)

In simpler terms:

If you increase the temperature of a gas while keeping the pressure constant, the volume of the gas will also increase proportionally. Conversely, if you decrease the temperature, the volume will decrease proportionally.