Current Electricity

Two cells are connected in opposition as shown. Cell \(\mathrm{E}_1\) is of \(8 \mathrm{~V}\) emf and \(2 \Omega\) internal resistance; the cell \(\mathrm{E}_2\) is of \(2 \mathrm{~V}\) emf and \(4 \Omega\) internal resistance. The terminal potential difference of cell \(\mathrm{E}_2\) is __________ V.