Q. A wire of length $100\ cm$ is connected to a cell of $emf\ 2\ V$ and negligible internal resistance. The resistance of the wire is $3\ \Omega.$ The additional resistance required to produce a potential drop of $1\ milli\ volt$ per $cm$ is
A) $60\ \Omega$
B) $47\ \Omega$
C) $57\ \Omega$
D) $35\ \Omega$
Explanation
(c) Potential gradient $x = \frac{e}{(R + R_{h} + r)}.\frac{R}{L}$
$\Rightarrow \frac{10^{- 3}}{10^{- 2}} = \frac{2}{(3 + R_{h} + 0)} \times \frac{3}{1} \Rightarrow R_{h} = 57\Omega$
Reviewed by Dr. Abubacker
Physics Educator & NEET/JEE Specialist
Ph.D. in Physics with 19+ years of teaching experience.