Series combination of cells :

# Series combination of cells : 

In this combination cathode of first cell is joined with anode of second cell, cathode of second cell with anode of third cell and so on. Finally an external resistance is joined between anode of first cell and cathode of Last cell along with key

let us considered a set of n cell connected in series, the EMF and external resistance of each cell be E and r respectively and the extender distance R is connected in a circuit

∵ EMF of each cell = E volt
∴ Total emf of n cell connected in Series= nE

∵ Internal resistance of each cell. = r ohm
Then equivalent internal resistance of n-cells are joined in series will be
r' = r+r+r+r+r........up to n terms
r' = nr ohm

∴ Total resistance of the circuit = R+r'
                                                      = (R+nr)

Current drawn from the battery
I = (Total emf) / (Total resistance)

I = nE / (R+nr) ..........(1)


Case(1) : If r<<R then we put r≈o in eqn(1)

I = nE / R + n(0)
I = nE / R
I = n(E/R)
I = n×( current drawn from cell)

Case(2): If r>>R then we put R≈0 in enq(1)

I = nE /(0+nr)
I = nE/nr
I = E/r
I = current drawn from a cell

It is clear that cell should be connected in series combination when the internal resistance of a cell is much less than external resistance.