Since in series combination, the current through each resistance remains same. So, equivalent resistance of the circuit is given as R‌equivalent ‌=R+r1+r2 and equivalent emf, E‌equivalent ‌=2E+E=3E From Ohm's law, I =
E‌equivalent
R‌equivalent‌
⇒I=
3E
R+r1+r2
When potential difference is zero across the first cell, then potential positive terminal is equal to the potential at negative terminal. VP=VN 2E=Ir1 Substituting the values in the above equation, we get 2E=‌