The length of a metal wire is L1 when the tension is T1 and L2 when the tension is T2. The unstretched length of wire is
Let the initial length of the metal wire is L.
The strain at tension T1 is ΔL1 = L1 − L
The strain at tension T2 is ΔL2 = L2 − L
Suppose, the Young's modulus of the wire is Y, then
where, A is an cross-section of the wire, assume to be same at all the situations