A potentiometer consists of a fixed resistance of 2030Ω in series with a slide wire of resistance 4 Ωm-1 when the constant current flows in the potentiometer circuit a balance is obtained when (a) a Weston cell of the EMF 1.018 Volt is connected across the fixed resistance and 150cm of the slide wire and when (b) a thermocouple is connected across 125cm of the slide wire only. Find the current in the potentiometer circuit and the E.M.F of thermal couple.

Solution:

Let us consider I be the current following in the potentiometer wire, then

$I = \frac{{1.018}}{{2030 + 1.5 \times 4}} = \frac{{1.018}}{{2036}} = 2 \times {10^{ - 4}}A$

Now, E.M.F of the thermocouple = potential difference across 1.25m of wire

=I $ \times $ Resistance of 1.25m of wire

=0.5$ \times $10^-3 $ \times $ 1.25$ \times $ 4 = 2.5$ \times $10^-3V

Hence Current in the potentiometer in the circuit is 5 $ \times $ 10^-4A

And E.M.F of thermocouple is 2.5$ \times $10^-3V