Question

A potentiometer wire of length 300 cm is connected in series with a resistance 780 Ω and a standard cell of emf 4V. A constant current flows through potentiometer wire. The length of the null point for cell of emf20 mV is found to be 60 cm. The resistance of the potentiometer wire is _____ Ω.

Answer 1

$l = 300 \;cm$

$ε = Kx$

$20 \times 10^{-3}$

= $\bigg(\frac{4 \times R}{780 + R} \times \frac{1}{300}\bigg)60$

$R = 20$