Q. A potentiometer wire of length $1m$ and resistance $10\ \Omega$ is connected in series with a cell of $emf\ 2V$ with internal resistance $1\ \Omega$ and a resistance box including a resistance $R.$ If potential difference between the ends of the wire is $1\ mV,$ the value of $R$ is
A) $20000\ \Omega$
B) $19989\ \Omega$
C) $10000\ \Omega$
D) $9989\ \Omega$
Explanation
(b) $V = i.R. = \frac{e}{(R + R_{h} + r)}.R \Rightarrow 10^{- 3} = \frac{2}{(10 + R + r)} \times 10$
$\Rightarrow R = 19,989\Omega$
Reviewed by Dr. Abubacker
Physics Educator & NEET/JEE Specialist
Ph.D. in Physics with 19+ years of teaching experience.