This is because of continuous usage, the wire loses its elasticity and does not regain it original dimension.
i.e: Length. Because of this, it shows wrong readings.     

Hooke's law of elasticity states that within the elastic limit, the strain produced in a body is directly proportional to the stress applied.
strain ∝ stress

(i) stress = \(\frac { F }{ A } = \frac { 980 }{ { 10 }^{ -6 } } =98\times { 10 }^{ 7 }N \ m^{ -2 }\)
(ii) strain \(=\frac { stress }{ Y } =\frac { 98\times { 10 }^{ 7 } }{ 12\times { 10 }^{ 10 } } =8.17\times { 10 }^{ -3 }\)
(no units)
(iii) Since, volume = 2\(\times\)10^-6m³
Energy = \(\frac{1}{2}\) (stress\(\times\)strain) \(\times\)volume \(=\frac{1}{2}\)(98 \(\times\)10⁷ ) x (8.17\(\times\)10 ³) 2 x 10⁻⁶ = 8 J

By definition, K =\(\frac { \frac { F }{ A } }{ \frac { \Delta V }{ V } } =P\frac { V }{\Delta{V} }\)
\(K=\frac { { 10 }^{ 6 }\times 1 }{ 1.5\times { 10 }^{ -5 } } =6.67\times { 10 }^{ 10 }{ N \ m }^{ -2 }\)

In a solid, interatomic forces bind two or more atoms together and the atoms occupy the positions of stable equilibrium. When a deforming force is applied on a body, its atoms are pulled apart or pushed closer. When the deforming force is removed, interatomic forces of attraction or repulsion restore the atoms to their equilibrium positions. If a body regains its original shape and size after the removal of deforming force, it is said to be elastic and the property is called elasticity. The force which changes the size or shape of a body is called a deforming force.
Examples: Rubber, metals, steel ropes.