The resistance of the meter bridge AB in given figure is $4 \Omega$. With a cell of emf $\varepsilon = 0.5 \mathrm {~V}$ and rheostat resistance $\mathrm { R } _ { \mathrm { h } } = 2 \Omega$ the null point is obtained at some point J. When the cell is replaced by another one of emf $\varepsilon = \varepsilon _ { 2 }$ the same null point J is found for $\mathrm { R } _ { \mathrm { h } } = 6 \Omega$. The emf $\varepsilon _ { 2 }$ is:\\
(1) 0.4 V\\
(2) 0.3 V\\
(3) 0.6 V\\
(4) 0.5 V