When 0.5A current is drawn from a cell, its potential difference is 1.8Vwhich reduces to 1.6V on drawing a current of 1.0A. The e.m.f. of the cell is:
For a cell, a graph is plotted between the potential difference V across the terminals of the cell and the current I drawn from the cell. The e.m.f and internal resistance of the cell is E and r , respectively.