$n$ identical cells are joined in series,with two cells $A$ and $B$ in the loop having reversed polarities. The $EMF$ of each cell is $E$ and the internal resistance is $r$. The potential difference across cell $A$ or $B$ is (where $n > 4$):

When two identical cells are connected either in series or in parallel across a $2 \ \Omega$ resistor,they send the same current through it. The internal resistance of each cell is: (in $Omega$)

In the given diagram,an ideal voltmeter $V$ reads $1.45\,V$. Then the relation between $r_1$ and $r_2$ is:

Two cells of emfs $1$ $V$ and $2$ $V$ and internal resistances $2 \Omega$ and $1 \Omega$ respectively are connected in parallel and provide a current of $1$ $A$ through an external resistance. If the polarity of one cell is reversed,the current through the external resistance becomes $\frac{\alpha}{5}$ $A$. The value of $\alpha$ is . . . . . . .

If six identical cells each having an $e.m.f.$ of $6\,V$ are connected in parallel,the $e.m.f.$ of the combination is ................ $V$.

Two batteries of different $e.m.f.$ values and internal resistances are connected in series with each other and with an external load resistor. The current is $3.0 \,A$. When the polarity of one battery is reversed,the current becomes $1.0 \,A$. The ratio of the $e.m.f.$ values of the two batteries is ............