Two batteries of emf's ε1 and ε2 are connected in a circuit as shown in figure. The galvanometer is kept undeflected always. Here AB=l. When the switch S is connected to point S1, BP=x1 and when the switch S is connected to point S2, BP=x2. Here, the ratio of emf's of the two batteries, i.e., ε1/ε2 equal/s :