AIPMT 2014 Physics and Chemistry Paper

A potentiometer circuit has been set up for finding the internal resistance of a given cell. The main battery used across the potentiometer wire, has an emf 2.0V and a negligible internal resistance. The potentiometer wire itself is 4m long, When the resistance R, connected across the given cell, has values of.
(i) infinity (ii) 9.5Ω
The balancing lengths', on the potentiometer wire are found to be 3m and 2.85m, respectively. The value of internal resistance of the cell is