A metal bar of length L and area of cross-section A is rigidly clamped between two walls. The Young's modulus of its material is Y and the coefficient of linear expansion is $\mathrm{\alpha }$. The bar is heated so that its temperature increases by $\mathrm{\theta }$°C. Then the force exerted at the ends of the bar is given by

• A

  $\mathrm{YL\alpha \theta }$

• B

  $\mathrm{YL\alpha \theta }/\mathrm{A}$

• C

  $\mathrm{YA\alpha \theta }$

• D

  $\mathrm{Y\theta \alpha }/\mathrm{LA}$