General Laws of Expansion and Compression

The general law of expansion or compression of a perfect gas is   

PVⁿ = Constant

It gives the relationship between the pressure and volume of a given quantity of gas. The value of n depends upon the nature of the gas and condition under which the changes (i.e. expansion or compression) takes place. The value of n may be between zero and infinity. But the following values of n are important from the subject point of view: 

• When n=0, then PV⁰ = Constant, i.e. P = Constant. In other words, for the expansion or compression of a perfect gas at constant pressure, n=0.
• When n=1, then PV = Constant, i.e. the expansion or compression is iso-thermal or hyperbolic.
• When n lies between 1 and n, the expansion or compression is polytropic, i.e PVⁿ = Constant.
• When n=γ, the expansion or compression is adiabatic, i.e PV^γ = Constant.
• When n=∞, the expansion or compression is at constant volume, i.e V = Constant.