In a potentiometer experiment, the balancing length of a cell is 560 cm. When an external resistance of 10 Ω is connected in parallel to the cell, the balancing length chages by 60 cm. The internal re

Question

In a potentiometer experiment, the balancing length of a cell is 560 cm. When an external resistance of 10 Ω is connected in parallel to the cell, the balancing length chages by 60 cm. The internal resistance of a cell is

TestHub · Accepted Answer

Consider a cell of emf E and balancing length $l_{1}$

$E = k l_{1}$

The potential difference is balanced by length $l_{2}$ .

$V = k l_{2}$

The internal resistance of the cell is given by

$r = (\frac{E - V}{V}) R = (\frac{E}{V} - 1) R = (\frac{l_{1}}{l_{2}} - 1) R$

$= (\frac{560}{560 - 60} - 1) 10 = (\frac{56}{50} - 1) 10$

$= \frac{6}{5} = 1.2 Ω$

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