Current Electricity

A potentiometer wire of length \(4 \mathrm{~m}\) and resistance \(5 ~\Omega\) is connected in series with a resistance of \(992 ~\Omega\) and a cell of e.m.f. \(4 \mathrm{~V}\) with internal resistance \(3 ~\Omega\). The length of \(0.75 \mathrm{~m}\) on potentiometer wire balances the e.m.f. of