If the external resistance is R and the internal resistance is r, the total resistance of the circuit is R+r, so that the current that flows is E/(R+r). If we take the point A as h...If the external resistance is R and the internal resistance is r, the total resistance of the circuit is R+r, so that the current that flows is E/(R+r). If we take the point A as having zero potential, we see that the potential of the point B will be E - Ir, and this, then, is the potential difference across the poles of the cell when a current I is being taken from it.
