Figure shows the circuit diagram of a potentiometer for determining the emf E of a Cell of negligible internal resistance.
(i)What is the purpose of using high resistance R2?
(ii) How does the position of balance point (J) change when the resistance R1 is decreased?
(iii) Why cannot the balance point be obtained
(1) when the emf E is greater than 2V and
(2) when key (K) is closed?