A rod of length $1000mm$ and coefficient of linear expansion  $\alpha ={10}^{-4}$ per degree is placed symmetrically between fixed walls separated by $1001 mm.$ The Young’s modulus of the rod is ${10}^{11}N/m^2$ .If the temperature is increased by  ${20}^{0}C$, then the stress developed in the rod is (in  $N/m^2$)