There is no change in the volume of a wire due to change in its length on stretching. The Poisson's ratio of the material of the wire is
0.50
-0.50
+0.25
-0.25
Let D be the diameter and Y, the volume. ThenV=πD2L4There is no change in volume∴ 0=π2DdDL+πD2dLor (dD/D)(dL/L)=−0⋅5