The resistance of the meter bridge AB in given figure is 4 Ω. With a cell of emf ε=0.5 V and rheostat resistance R_h =2 Ω the null point is obtained…

The resistance of the meter bridge AB in given figure is $\displaystyle 4 \Omega$. With a cell of emf $\displaystyle \varepsilon=0.5 \mathrm{~V}$ and rheostat resistance $\displaystyle \mathrm{R}_{\mathrm{h}}=2 \Omega$ the null point is obtained at some point J. When the cell is replaced by another one of emf $\displaystyle \varepsilon=\varepsilon_2$ the same null point J is found for $\displaystyle \mathrm{R}_{\mathrm{h}}=6 \Omega$. The emf $\displaystyle \varepsilon_2$ is,