A solid steel cube constrained on all six faces is heated so that the temperature rises uniformly by $\Delta T$. If the thermal coefficient of the material is $\alpha$, Young's modulus is $E$ and the Poisson's ratio is $\upsilon$, the thermal stress developed in the cube due to heating is
- $-\dfrac{\alpha (\Delta T) E}{(1-2 \upsilon)} \\$
- $-\dfrac{2 \alpha (\Delta T) E}{(1-2 \upsilon)} \\$
- $-\dfrac{3 \alpha (\Delta T) E}{(1-2 \upsilon)} \\$
- $-\dfrac{\alpha (\Delta T) E}{3 (1-2 \upsilon)}$