The resistance of the meter bridge AB in given figure is $$4\Omega$$. With a cell of emf $$\varepsilon = 0.5$$ V and rheostat resistance $$R_h = 2\Omega$$ 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 $$R_h = 6\Omega$$. The emf $$\varepsilon_2$$ is:

A

0.4 V

B

0.3 V

C

0.6 V

D

0.5 V