1.

The thermo e.m.f. of a thermo- couple is `25 muV//^@C` at room temperature. A galvanometer of 40 ohm resistance, capable of detecting current as low as `10^(-5)`A, is connected with the thermo couple. The smallest temperature difference that can be detected by this system isA. `16^(@)C`B. `12^(@)C`C. `8^(@)C`D. `20^(@)C`

Answer» Correct Answer - A
Thermo-emf of thermocouple is `=25 mu V//^(@)C`
`:.` After connecting the thermocouple with the galvanometer, thermo-emf
`E=25 muV//^(@)Cxx(theta^(@)C)impliesE=250xx10^(-6)V`
Potential drop developed across the galvanometer `=iR=10^(-5)xx40=4xx10^(-4)` volt
`:. 4xx10^(-4)=250xx10^(-6)`
`theta=4/25xx10^(2)=16^(@)C`


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