The opposition offered by the electrolyte of the cell to the flow of electric current through it is called the internal resistance of the cell.
Factors affecting Internal Resistance of a cell:
i) Larger the separation between the electrodes of the cell, more the length of the electrolyte through which current has to flow and consequently a higher value of internal resistance.
ii) Greater the conductivity of the electrolyte, lesser is the internal resistance of the cell. i.e. internal resistance depends on the nature of the electrolyte.
iii) The internal resistance of a cell is inversely proportional to the common area of the electrodes dipping in the electrolyte.
iv) The internal resistance of a cell depends on the nature of the electrodes.
Consider the following figure:
E = V + v
= IR + Ir
= I (R + r)
I = E / (R + r)
This relation is called circuit equation