A battery of 24 cells, each of emf 1.5V and internal resistance $2\mathrm{\Omega }$ is to be connected in order to send the maximum current through a $12\mathrm{\Omega }$ resistor. The correct arrangement of cells will be.

Suppose m rows are connected in 
parallel and each row contains n identical cells 
(each cell having $\mathrm{E}=15\mathrm{V}\mathrm{and}\mathrm{r}=2\mathrm{\Omega }$ ). For maximum current in the  external  
resistance R, the necessary condition is  

$\mathrm{R}=\frac{\mathrm{nr}}{\mathrm{m}}$

$\Rightarrow 12=\frac{\mathrm{n}\times 2}{\mathrm{m}}\Rightarrow \mathrm{n}=6\mathrm{m}$  -----(i)

Total cells = 24=$\mathrm{n}\times \mathrm{m}$ -------(ii)
On solving equations (i)&(ii)   
$\mathrm{n}=12\mathrm{m}=2$

i.e 2 rows of 12 cells are connected in 
parallel.