in measuring unknown emf by potentiometer, why must the stable current source(working battery) have a voltage greater than any voltage to be measured? i cant understand why.. in our exercise in physics, we used a slide-wire potentiometer with the assumption that 1 meter of the slide-wire gives a voltage drop of 1V. so, the battery we used has an emf slightly greater than 2 volts. is there a connection between the length of the slide wire used and the use of a battery with an emf greater than 2V? i am currently doing our physics lab report and honestly, its part of the discussion. im asking for help for i cant understand. tanx to anybody who dares to reply..