Question

The balancing length for a cell is 560 cm in a potentiometer experiment. When an external resistance of 10 ohm is connected in parallel to the cell the balancing length changes by 60 cm. The internal resistance of the cell in ohms is

• A. 1.6
• B. 1.4
• C. 1.2
• D. 0.12

Answer 1

The correct option is C 1.2

$\frac{r}{R}=\frac{l_1-l_2}{l_2}$
here R=10 ohm
$l_1$ = 560 cm
$l_2$ =560-60=500 cm
$r=R\times \left(\frac{l_1-l_2}{l_2}\right)$
$=10\times \left(\frac{560-500}{500}\right)$
=1.2 ohm