It is a quantitative relationship between temperature and volume of a gas and was given by french scientists J.Charles in 1787.
Charles Law States:
“The Volume of the given mass of a gas is directly proportional to the absolute temperature when the pressure is kept constant.”
V = kT
V/T = k
If the temperature is changed from T1 to T2 and volume changes from V1 to V2, then:
V1/T1 = k and V2/T2 = k
V1/T1 = V2/T2
The ratio of volume to temperature remains constant for same amount of gas at same pressure.
This was observe by J.Charles in 1787 that if we give temperature to gas present in container then the piston place up the container will move upward hence the volume of container increases when pressure kept constant.