What is emf of a cell?

How can a continuous flow of current be obtained? What are the sources of energy and name of the devices required for continuous flow of current?

How much work is done in moving a charge of $2 \mathrm{C}$ across two points having a potential difference $10 \mathrm{V}$?

Mention one similarity and one dissimilarity between electromotive force and potential difference. 

Two cells of the same EMF $E$ but different internal resistances $r_1$ and $r_2$ are connected in series with an external resistance $R$ as shown in the figure. The terminal potential difference across, the second cell is found to be zero. The external resistance $R$ must then be:

A battery of e.m.f $12 \mathrm{V}$ and internal resistance $0.5 \mathrm{\Omega }$ is charged by a battery charger which supplies a $132 \mathrm{V}$ d.c. supply using a series resistance of $11.5 \mathrm{\Omega }$. What is the terminal voltage of the battery during charging?