A potentiometer wire 10 m long has a resistance of 40Ω. It is connected in series with a resistance box and a 2V storage cell. If the potential gradient along the wire is 0.1 mV/cm , the resistance in the box is
Answer & explanation
Correct answer: option 2
$\text{Potential Gradient is } 0.1 mV/cm = 0.01 V/m$
$\text{Total Potential difference acroee Potentiometer wire is }V = 0.01\times 10V =0.1 V= 40I$
$ I = \frac{1}{400}$
$ Also , 2V = I(R+ 40) $
$ R = \frac{2}{I} - 40 = 800 - 40 = 760 \Omega$