When a resistance of $2\,\Omega$ is connected across the terminals of a cell,the current is $0.5\,A$. When the resistance is increased to $5\,\Omega$,the current is $0.25\,A$. The internal resistance of the cell is ............. $\Omega$.

Two sources of equal $emf$ $(\varepsilon)$ are connected in series to an external resistance $R$. The internal resistances of the two sources are $R_1$ and $R_2$ $(R_2 > R_1)$. If the potential difference across the source having internal resistance $R_2$ is zero, then:

The internal resistance of a cell is the resistance of

Two cells with same emf $E$ but different internal resistances,$r_1$ and $r_2$,are connected in series to an external resistance $R$. If the potential difference across the first cell is zero,then the value of $R$ is

Two batteries of emf $\varepsilon_1$ and $\varepsilon_2$ (where $\varepsilon_2 > \varepsilon_1$) and internal resistances $r_1$ and $r_2$ respectively are connected in parallel as shown.

Consider a parallel combination of the cells shown in the figure. The potential difference between $B_1$ and $B_2$ is