ab is a potentiometer wire?
AB is a potentiometer wire of length 100 cm and resistance 10 ohms. It is connected in series with a resistance R=40 ohms and a battery of e.m.f. 2 V and negligible internal resistance. If a source of unknown e.m.f. E is balanced by 40 cm length of the potentiometer wire, the value of E is :- A .