a long bar have a length L and radius r then volume

Differentiating both the sides

Dividing both the sides by volume of bar

Þ         Volumetric strain = longitudinal strain + 2(lateral strain)

Important points:

(i) If a material having s = – 0.5 then =0

Volume = constant  or  K = ¥ i.e., the material is incompressible.

(ii) If a material having s = 0, then lateral strain is zero i.e. when a substance is stretched its length increases without any decrease in diameter e.g. cork. In this case change in volume is maximum.

(iii) Theoretical value of Poisson’s ratio

(iv) Practical value of Poisson’s ratio