AB is a potentiometer wire (figure). If the value of R is increased, in which direction will the balance point J shift?
Hint: The potential drop across Ab is directly proportional to the length of the wire.
Step 1: Find the potential drop across AB.
With the increase of R, the current in the main circuit decreases which in turn, decreases the potential difference across AB, and hence potential gradient (k) across AB decreases.
Step 2: Find the final position of the balance point.
Since, at the neutral point, for a given emf of a cell, l increase as the potential gradient (k) across AB has decreased because,
E = kl
Thus, with the increase of l, the balance point will shift towards B.
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