Near room t emperature, the thermo emf of a copper constantan couple is `40 muV` per degree. What is the smallest temperature difference that can be detected with a single such couple and a galvanometer of 100 ohm resistance capable of detecting current as low `10^(-6)` ampere?

Explanation

Let `0^(@)C` be the smallest temperature that can be measured.
Corresponding thermo emf=`40xxthetamuV=40xxthetaxx10^(-6)V`
Resistance of the galvanometer `=100Omega`
Smallest current that can be detected, `I=10^(-6)A`
current `=(emf)/("Resistance")` or `10^(-6)=(40xxthetaxx10^(-6))/(100)` or `theta=(10^(-6)xx100)/(40xx10^(-6)).^(@)C=2.5^(@)C`.