## Sunday, 14 February 2016

In our previous post, we were concentrated over the one equation of state for a perfect gas i.e. Boyle’s Law. Today we will start our discussion with another equation of state for a perfect gas i.e. Charles law.

### Charles law

Gases have various important properties or variables such as pressure, volume, mass and temperature. These variables of gases are related with each other and magnitude of these variables or properties will determine the state of gas.

Charles and Gay Lussac’s, scientists, had investigated the relationship between volume and temperature of a gas by keeping mass and pressure of gas constant.

Charles law describes the behavior of expansion of gases when heated or describes the behaviour of contraction of gases when cooled.

According to Charles law, if any fixed mass of gas is heated at constant pressure, changes in volume of gas will be directly proportional with temperature.

If absolute temperature of the gas is T and volume of the gas is V, at constant pressure and for a fixed mass of gas, we will have following relationship between absolute temperature T and volume V.

### Let us understand Charles law with the help of below figure

Fixed mass of a gas is contained in jar which has a provision of heating by torch provided below the jar. Volume of the gas could be changed by changing the position of piston with the help of screw provided at the top of piston. We can see here that variation of volume with respect to temperature is linear.

According to Charles law, if at initial state absolute temperature of gas is 200 K and volume is 5 m3. Let we have heated the gas up to a temperature of 400 K, then volume of the gas will also be increased up to 10 m3.

We will continue our discussion further with another engineering topic i.e. What is first law of thermodynamics?