# Other ways of expressing Charles’s law and the Pressure law

Other ways of expressing Charles’s law and the Pressure law

If we assume that the two graphs in Figs. 16.8 and 16.9 have been plotted using Celsius and thermodynamic temperatures then we can use them to express Charles’s

law and the Pressure law in a form which is usually more convenient for calculation purposes than the statements of the laws given on pages 175 and 177. In the volume-temperature graph, any pair of triangles such as ABC, ADE are similar and therefore,

But the lengths of these sides represent volumes and corresponding absolute or thermodynamic temperatures to scale.

Hence,
V/V2 -=-T/T2

This applies to all values of volume and thermodynamic temperature and so we can say,

VT = constant

Similarly, from the pressure-temperature graph we may show that

p/T = constant

These two equations enable us to state the gas laws in the following forms, which should be compared with those given previously on pages 175 and 177.