In the potentiometer, when the cell in the secondary circuit is shunted with 
resistance, the balance is obtained at the length 120 cm of wire. Now when the same cell is shunted with 
resistance, the balance is shifted to a length of 180 cm. The internal resistance of cell is 
Text Solution
Verified by ExpertsA
In a potentiometer, the internal resistance 
of a cell is given by the formula 
, where 
is the balancing length in open circuit, 
is the balancing length when shunted with resistance 
.
This can be rewritten as 
or 
.
Case 1: 
and 
.
……….. (i)
Case 2: 
and 
.
………. (ii)
Dividing equation (ii) by (i):
The internal resistance of the cell is 
.
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