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 is

Options

A. `16^@C`
B. `12^@C`
C. `8^@C`
D. `20^@C`

Answer

A

Explanation

(a) Let `theta` be the smallest temperature difference that can be detected by the thermocouple, then
`I xx R = (25 xx 10^(-6)) theta`
where I is the smallest current which can be detected
by the galvanometer of resistance R.
`:. 10^(-5) xx 40 = 25 xx 10^(-6) xx theta`
`:. theta = 16^@C`.