To get the maximum current from a parallel combination of $n$ identical cells,each of internal resistance $r$,connected to an external resistance $R$,which of the following conditions must be satisfied?

Infinite number of cells having $emf$ and internal resistance $(E, r)$,$(\frac{E}{n}, \frac{r}{n})$,$(\frac{E}{n^2}, \frac{r}{n^2})$,$(\frac{E}{n^3}, \frac{r}{n^3})$... are connected in series across an external resistance of $\frac{nr}{n+1}$. The current flowing through the external resistor 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 . . . . . . .

Explain cell,emf,and internal resistance. Derive the relation between potential difference,emf,and internal resistance.

What will be the reading of the voltmeter in the given circuit (in $V$)?

The variation of terminal potential difference $(V)$ with current $(I)$ flowing through a cell is as shown in the graph. The $EMF$ $(E)$ and internal resistance $(r)$ of the cell are: