Question

In a Potentiometer experiment the balancing length with a cell is $560\, cm$, when an external resistance of $10\, \Omega$ is connected in parallel to the cell, the balancing length changes by $60\, cm$. Find the internal resistance of the cell

• A. $1\, \Omega$
• B. $2\, \Omega$
• C. $1.2\, \Omega$
• D. $2.1\, \Omega$

Answer 1

Answer: (C)

Given, $l_{1}=560\, cm,\, R=10\, \Omega$
$l_{2}=l_{1}-60$
$\Rightarrow l_{2}=560-60=500\, cm$
$\therefore $ Internal resistance of cell is given by
$r =\left(\frac{l_{1}-l_{2}}{l_{2}}\right) R=\left(\frac{560-500}{500}\right) 10$
$=\frac{60}{500} \times 10=\frac{6}{5}=1.2\, \Omega$