In a Potentiometer experiment the balancing length with a cell is 560 cm. When an external resistance of 10 Ω is connected…

Q: In a Potentiometer experiment the balancing length with a cell is 560 cm. When an external resistance of 10 Ω is connected in parallel to the cell, the balancing length changes by 60 cm. Find the internal resistance of the cell.

Sol. Balancing length l1 = 560 cm

Change in balancing length (l1-l2) = 60 cm

560 – l2 = 60

∴ l2 = 500 cm

$\large r = ( \frac{l_1}{l_2} – 1 )R$

$\large r = ( \frac{560}{500} – 1 )\times 10$

r =1.2 Ω