Question 5: Under what circumstances can the terminals P.D of a battery exceeds its emf?
Terminal Potential Difference can be small, equal or more than the emf of the source. When the circuit is open (no load) the emf and terminal voltage are same, when there is load resistance in the circuit, terminal voltage is less than the emf. However, terminal voltage will exceed the emf of the battery when current is driven backward through the battery; when it enters the positive terminal and leaves at negative terminal. This is possible when we put the battery to charge. In such a situation, the terminal potential is larger than the emf. Since the current flows in the reverse direction in the battery, therefore, the potential drop is positive and
So the terminal potential is larger than the emf by an amount Ir.