1) In a potentiometer experiment, the balancing length of a cell is 560 cm. When an external resistance of 10 Ω is connected in parallel to the cell, the balancing length changes by 60 cm. The internal resistance of a cell is A) 1.4Ω B) 1.6Ω C) 0.12Ω D) 1.2Ω Answer: Option DExplanation: Let us consider a cell of emf E and balancing length l1 E=kl1 potential difference is balanced by length l2 , V= kl2 r=(E−VV)R=(EV−1)R=(l1l2−1)R r=(560560−60−1)10=(5650−1)10=65=1.2 Ω