A cell of emf $E$ is connected across a resistance $R$. The potential difference between the terminals of the cell is found to be $V$. Then the internal resistance of the cell must be

If the potential difference across the internal resistance $r_1$ is equal to the emf $E$ of the battery, then

Two batteries of emf ${\epsilon }_1$, and ${\epsilon }_2\left({\epsilon }_2>{\epsilon }_1\right)$and internal resistances $r_1$ and $r_2$ respectively are connected in parallel as shown in figure