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 of 2.0 v and a negligible internal resistance .The potentiometer wire itself is 4 m long . When the resistance , R connected across the given cell, has values of (i) Infinity , (ii) `9.5 Omega` the balancing length's on the potentiometer wire are found to be 3 m and 2.85 m , respectively . The value of internal resistance of the cell is .

Options

A. `0.5 Omega`
B. `0.75 Omega`
C. `0.3 Omega`
D. `0.95 Omega`

Answer

A

Explanation

`R = 9.5 Omega, l_(1) = 3m, l_(2) = 2.85 m`
`r = R(l_(1)/l_(2)-1) = 9.5 (3/2.85-1) = 0.5 Omega`