To get maximum current through a resistance of $2.5\,\Omega$,one can use $m$ rows of cells,each row having $n$ cells. The internal resistance of each cell is $0.5\,\Omega$. What are the values of $n$ and $m$ if the total number of cells is $45$?

Each cell has emf $1.5 \ V$ and internal resistance $1 \ \Omega$. The minimum number of such cells required to produce a maximum current of $1.5 \ A$ in an external load resistance of $30 \ \Omega$ is

Two cells are connected in opposition as shown. Cell $E_1$ has an electromotive force (emf) of $8 \ V$ and an internal resistance of $2 \ \Omega$; cell $E_2$ has an emf of $2 \ V$ and an internal resistance of $4 \ \Omega$. The terminal potential difference of cell $E_2$ is: (in $V$)

When can the internal resistance of a cell be neglected? Explain.

$A$ student is given $4$ identical batteries having $EMF$ $1.5 \ V$ each and internal resistance of $0.1 \ \Omega$ each. The student is asked to connect them in an assisting manner. By mistake,he connects $1$ battery in reverse way. The resultant $EMF$ and resultant internal resistance offered by the combination is . . . . . . .

Four identical cells, each of $2 \, V$ e.m.f., are connected in parallel. They supply current to an external circuit consisting of two $15 \, \Omega$ resistors connected in parallel. The terminal voltage of the equivalent cell, as measured by an ideal voltmeter, is $1.6 \, V$. Calculate the internal resistance of each cell in $\Omega$.