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

Question

( A ) $20^{\circ}C$
( B ) $8^{\circ}C$
( C ) $16^{\circ}C$
( D ) $12^{\circ}C$