thermocouple Questions

The thermo e.m.f. of a thermo-couple is $25\mu {\text{V/}}^{\circ }\text{C}$ at room temperature. A galvanometer of $40\Omega$ resistance, capable of detecting current as low as $10^{-5}\text{A}$, is connected with the thermocouple. The smallest temperature difference that can be detected by this system is: