A temperature difference can generate e.m.f. in some materials. Let $$S$$ be the e.m.f. produced per unit temperature difference between the ends of a wire, $$\sigma$$ the electrical conductivity and $$\kappa$$ the thermal conductivity of the material of the wire. Taking $$M$$, $$L$$, $$T$$, $$I$$ and $$K$$ as dimensions of mass, length, time, current and temperature, respectively, the dimensional formula of the quantity $$Z = \frac{S^2 \sigma}{\kappa}$$ is: