A potentiometer wire of length 100 cm has a resistance of 10 
. It is connected in series with a resistance and a cell of emf 2 V and of negligible internal resistance. A source of emf 10 mV is balanced against a length of 40 cm of the potentiometer wire. What is the value of external resistance?
Text Solution
Verified by ExpertsA
The current in the potentiometer wire AC is
The potential difference across the potentiometer wire is
V = current × resistance
The length of the wire is, l = 100 cm.
So, the potential gradient along the wire is
…(i)
The source of emf 10 mV is balanced against a length of 40 cm of the potentiometer wire
i.e., 
or 
(Using (ii))
or 
.
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