$EMF$ is most closely related to

$A$ cell of e.m.f. $E$ is connected with an external resistance $R$,then the potential difference across the cell is $V$. The internal resistance of the cell will be:

Two cells $E_1$ and $E_2$ having equal $EMF$ $E$ and internal resistances $r_1$ and $r_2$ $(r_1 > r_2)$ respectively are connected in series. This combination is connected to an external resistance $R$. It is observed that the potential difference across the cell $E_1$ becomes zero. The value of $R$ will be

Each of the six ideal batteries of emf $20 \, V$ is connected to an external resistance of $4 \, \Omega$ as shown in the figure. The current through the resistance is (in $ \, A$)

Two cells $P$ and $Q$ each of emf $2.16 \text{ V}$ are connected in series with a resistor of $19.6 \text{ } \Omega$. An ideal voltmeter reads $2 \text{ V}$ when connected across the cell $P$ and $1.92 \text{ V}$ when connected across the cell $Q$. The ratio of the internal resistances of the cell $P$ and $Q$ 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 ................ $V$.