A Wheatstone bridge is used to determine the value of unknown resistance X by adjusting the variable resistance Y as shown in the figure. For the most precise measurement of X, the resistance P and Q

 

Load of mass will be equally distributed among the four colours so force on each columns will be 125 × 10³ N.

Cross section area of the column = $\pi \left[{\left(1\right)}^2-{\left(0.5\right)}^2\right]=2.355m^2$

Using young’s modulus :  $\epsilon =\frac{\sigma }{Y}=\frac{F}{AY}=\frac{125\times 10^3}{2.355\times 2\times 10^{11}}=2.65\times 10^{-7}$