Question

$24$ cells of emf $1.5\,V$ each having internal resistance of $1$ ohm are connected to an external resistance of $1.5$ ohms . To get maximum current

• A. all cells are connected in series combination
• B. all cells are connected in parallel combination
• C. 4 cells in each row are connected in series and6 such rows are connected in parallel
• D. 6 cells in each row are connected in series and 4 such rows are connected in parallel

Answer 1

Answer: (D)

6 cells in each row are connected in series and 4 such rows are connected in parallel

Answer 2

For series, $i=\frac{n E}{n r +R}$
$i=\frac{24 \times 1.5}{24+1.5}=1.41$
For parallel, $i=\frac{E}{\frac{r}{n}+R}$
$i=\frac{1.5}{\frac{1}{24}+1.5}$
For $4 \times 6$ combination $i =\frac{n E}{R+\frac{n r}{m}}$
$i =\frac{4 \times 1.5}{1.5+\frac{4}{6}}=2.77$
For $6 \times 4$ combination
$i=\frac{n E}{R+\frac{n r}{M}}$
$\Rightarrow i=\frac{6 \times 1.5 \times 4}{12}=3$