$A$ battery of emf $18 \, V$ and internal resistance $3 \, \Omega$ and another battery of emf $10 \, V$ and internal resistance $1 \, \Omega$ are connected in parallel as shown in the figure. The voltmeter reading is: (in $ \, V$)

Write the equation for the equivalent electromotive force (emf) of a series connection of cells.

When two cells of emfs $E_1$ and $E_2$ and different internal resistances $r_1$ and $r_2$ are connected in series with an external load resistor $R$,the current through the load is $5 \ A$. If the polarity of the cell of emf $E_2$ is reversed,then the current through the load is $2 \ A$. Then $\frac{E_1}{E_2} = $

$(a)$ 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?

$A$ total of $100$ cells,each having an $emf$ of $5\,V$ and an internal resistance of $1\,\Omega$,are connected to an external resistance of $25\,\Omega$ to obtain the maximum current. If each row contains an equal number of cells,what should be the number of rows?