$A$ total of $100$ cells,each having an $emf$ of $5\,V$ and an internal resistance of $1\,\Omega$,are connected to an external resistance of $25\,\Omega$ to obtain the maximum current. If each row contains an equal number of cells,what should be the number of rows?

Two cells are connected between points $A$ and $B$ as shown. Cell $1$ has an emf of $12 \, V$ and an internal resistance of $3 \, \Omega$. Cell $2$ has an emf of $6 \, V$ and an internal resistance of $6 \, \Omega$. An external resistor $R$ of $4 \, \Omega$ is connected across $A$ and $B$. The current flowing through $R$ will be $............. \, A$.

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.

$A$ cell $E_{1}$ of $emf 6 V$ and internal resistance $2 \Omega$ is connected with another cell $E_{2}$ of $emf 4 V$ and internal resistance $8 \Omega$ as shown in the figure. The potential difference across points $X$ and $Y$ is............ $V$.

$A$ storage cell is charged by $5\, A$ $D.C.$ for $18\, hours$. Its strength after charging will be .............. $AH$.

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: