A potentiometer circuit has been setup for finding. The internal resistance of a given cell. The main battery used a negligible internal resistance. The potentiometer wire itsefl is `4 m` long. When the resistance, `R`, connected across the given cell, has value of
(i) Infinity `9.5 Omega`,
(ii) the 'balancing length' , 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. `0.25 Omega`
B. `0.65 Omega`
C. `0.5 Omega`
D. `0.75 Omega`

Answer

c

Explanation

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