$10$ cells,each of $emf$ $E$ and internal resistance $r$,are connected in series to a variable external resistance. The figure shows the variation of the terminal potential difference of their combination with the current drawn from the combination. The $emf$ of each cell is ................ $V$.

For a cell,the terminal potential difference $(P.D.)$ is $2.2\;V$ when the circuit is open and reduces to $1.8\;V$ when the cell is connected to an external resistance of $R = 5\;\Omega$. Determine the internal resistance $(r)$ of the cell.

The reading of a high resistance voltmeter when a cell is connected across it is $2.2\, V$. When the terminals of the cell are also connected to a resistance of $5\,\Omega$,the voltmeter reading drops to $1.8\, V$. Find the internal resistance of the cell in $\Omega$.

In the given circuit,if $V_{AB} = 4\ V$,then the value of resistance $X$ in ohms will be:

$A$ 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 . . . . . . .

$A$ battery consists of $5$ rows of cells,each row containing $10$ cells in series. This battery is connected in parallel to an external resistor of $20 \,\Omega$. If each cell has an $emf$ of $1.5 \,V$ and an internal resistance of $1 \,\Omega$,what is the current $i$ flowing through the external resistor (in $,A$)?