To get maximum current through a resistance of 2.5 W, one can use m rows of cells, each row having n cells. The internal resistance of each cell is 0.5 W. What are the values of n and m, if the total number of cells is 45.

Since total number of cell is 45, mn = 45. Now n cells are in series, then resistance is n × 0.5 W . Now there are m rows with such series, then $\frac{1}{R_{eq}}=\frac{1}{n\times 0.5}+\frac{1}{n\times 0.5}+\mathrm{......}\left(mtimes\right)$$R_{eq}=\frac{n\times 0.5}{m}=2.5\Omega$. $\left[\because I=\frac{nE}{R+r_{eq}}\right]$.Using Eqs, m = 3 and n = 15.