Physical significance of ‘a’:

‘a’ is a measure of the magnitude of intermolecular attractive forces within a gas. This implies that if a molecule has a large value of a then the intermolecular forces of attraction between its molecules will be large and hence it could be easily liquefied.

Physical significance of ‘b’:

‘b’ is a measure of the volume of a gas molecule. It gives us the volume occupied by all the gaseous molecules contained in a given vessel which was earlier neglected according to kinetic theory and this correction term becomes more significant at high pressure as the molecules are themselves incompressible and occupy an appreciable fraction of the total volume.