Explain how the cells are grouped in series, Obtain the condition for maximum current through an external resistor.

Explanation

Cells in series. The cell are said to be connected in series, if we can proceed from one point to another through one path. Fig. shows the series combination of n cells. Here n cells, each of e.m.f. E and internal resistance r are connected to an external resistance R.

In series combination, the total e.m.f. of the cells is equal to the sum of the e.m.f.s of the individual cells.
`therefore` Total e.m.f. of the cells=nE
Since internal resistance of all the cells are also connected in series.
`therefore` Total internal resistance of the cell=nr
So current flowing through the circuit,
`I=(nE)/(R+nr)`
Case 1. if `R lt lt nr`, so `R=nrcongnr`
`thereforeI=(nE)/(nr)=(E)/(r)`
Case 2. if `R gt gt nr,` so `R+nrcongR`
`therefore I=(nE)/(R)=nxx`current due to single cell.
Thus in series combination of cells, to have maximum current, the total internal resistance of the cells should be negligible as compared to the external resistance of the circuit.