The thermo e.m.f. of a thermo-couple is \[25\mu V{{/}^{o}}C\] at room temperature. A galvanometer of 40 ohm 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 [AIEEE 2003]

• A.            \[{{20}^{o}}C\]                    
• B.            \[{{16}^{o}}C\]
• C.            \[{{12}^{o}}C\]                    
• D.            \[{{8}^{o}}C\]