Two batteries with different $emf$ and different internal resistances are connected as shown in the figure. The voltage between the two terminals $A$ and $B$ is ........ $volt$.

When does the current drawn from a cell become maximum?

$(a)$ Six lead-acid type of secondary cells each of $emf$ $2.0 \;V$ and internal resistance $0.015 \;\Omega$ are joined in series to provide a supply to a resistance of $8.5\; \Omega$. What are the current drawn from the supply and its terminal voltage?
$(b)$ $A$ secondary cell after long use has an $emf$ of $1.9 \;V$ and a large internal resistance of $380\; \Omega$. What maximum current can be drawn from the cell? Could the cell drive the starting motor of a car?

$A$ resistor of resistance $R$ is connected between the terminals of a cell of $\operatorname{emf} E$ and internal resistance $r$. If $I$ is the current through the circuit,the terminal potential difference of the cell is given by:

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

To draw maximum current from a combination of cells,how should the cells be grouped?