In a potentiometer experiment it is found that no current passes through the galvanometer when the terminals of the cell are connected across `0.52 m` of the potentiometer wire. If the cell is shunted by a resistance of `5Omega` balance is obtained when the cell connected across` 0.4m` of the wire. Find the internal resistance of the cell.

Options

A. `1Omega`
B. `1.5 Omega`
C. `2 Omega`
D. `2.5 Omega`

Explanation

With only the cell,
On balancing `E=52 times x`……….(i)
where x is the potential gradient of the wire
when the cell is shunted
Similarly on balancing
`V=E-(Er)/((R+r))=40 times x`……(ii)
Solving Eqs. (i) and (ii) we get
`E/V=1/(1-r/(R+r))=52/40 implies E/V=(R+r)/R=52/40 implies (5+r)/5=52/40 implies R=5/2 Omega r=1.5 Omega`