In a potentiometer of one metre length, an unknown emf voltage source is balanced at 60 cm length of potentiometer wire, while a 3 V battery is balanced at 45 cm length. Then, the emf of the unknown voltage source is:
4 V
We know,
emf ∝ balanced length:
E1=kl1E2=kl2E2=3 Vl1=60 cm,l2=45 cmE3=k×60k×45E=4 V