In the circuit shown in the figure below the cells ${\mathrm{E}}_1$ and ${\mathrm{E}}_2$ have e.m.f. $4 \mathrm{V}$ and $8\mathrm{ }\mathrm{V}$ and internal resistance $0.5\mathrm{ }\mathrm{\Omega }$ and $1.0\mathrm{ }\mathrm{\Omega }$ respectively. Then the potential difference across the cell ${\mathrm{E}}_1$ and ${\mathrm{E}}_2$ will be-