$A$ group of $N$ cells whose $emf$ varies directly with the internal resistance as per the equation $E_N = 1.5\, r_N$ are connected in series as shown in the figure. The current $I$ in the circuit is ........... $A$.

Four identical cells,each having an electromotive force $(e.m.f.)$ of $12\,V$,are connected in parallel. The resultant electromotive force $(e.m.f.)$ of the combination is .............. $V$.

For two cells having the same $EMF$ $E$ and internal resistance $r$, the current passing through an external resistor of $6 \ \Omega$ is the same when both cells are connected either in parallel or in series. The value of internal resistance $r$ is . . . . . . $ \ \Omega$.

$A$ battery of emf $18 \, V$ and internal resistance $3 \, \Omega$ and another battery of emf $10 \, V$ and internal resistance $1 \, \Omega$ are connected in parallel as shown in the figure. The voltmeter reading is: (in $ \, V$)

In an electric circuit,a cell of certain $emf$ provides a potential difference of $1.25\, V$ across a load resistance of $5\, \Omega$. However,it provides a potential difference of $1\, V$ across a load resistance of $2\, \Omega$. The $emf$ of the cell is given by $\frac{x}{10}\, V$. Then the value of $x$ is ..... .

The $n$ rows,each containing $m$ cells in series,are joined in parallel. Maximum current is drawn from this combination across an external resistance of $3 \,\Omega$. If the total number of cells used is $24$ and the internal resistance of each cell is $0.5 \,\Omega$,then: