a
Diameter $ d =0.5 mm$
$Y =2 \times 10^{11} N / m ^2$
Strain $=\frac{\text { Stress }}{ Y }$
$\frac{\Delta L }{ L }=\frac{ F }{ AY }$
$\Delta L =\frac{ FL }{ AY }=\frac{1.2 \times 10 \times 1}{3.2 \times \frac{\left(0.5 \times 10^{-3}\right)^2}{4} \times 2 \times 10^{11}}$
$\Delta L =\frac{12}{1.6 \times 0.25 \times 10^5}=30 \times 10^{-5}=0.3 mm$
$L.C.$ of Vernier scale $=0.1 mm$ Number of division which coincide with main scale $=3$.