\( \Rightarrow 1 \times {10^{11}} \times \left( {\frac{{1 \times {{10}^{ - 3}}}}{1}} \right) = 2 \times {10^{11}} \times \left( {\frac{{\Delta {L_s}}}{{0.5}}} \right)\)
\(\therefore \Delta {L_s} = \frac{{0.5 \times {{10}^{ - 3}}}}{2} = 0.25\,mm\)
Therefore, total extension of the composite
\(wire = \Delta {L_c} + \Delta {L_s}\)
\( = 1\,mm + 0.25\,m = 1.25\,m\)