A student uses the circuit diagram of a potentiometer as shown in the figure
(a) For a steady current I passing through the potentiometer wire, he gets a null point for the cell and not for
. Give the reason for this observation and suggest how this difficulty can be resolved.
(b) What is the function of resistance R used in the circuit? How will the change in its value affect the null point?
(c) How can the sensitivity of the potentiometer be increased?
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a) Both
have the positive terminal connected at A whereas negative terminal of 
is connected to A. So null point is not obtained for cell 2
By interchanging the terminal of
, the difficulty can be resolved.
b) The resistance R protects the galvanometer by reducing the current flowing through it. As the null point is obtained for zero galvanometer reading, change in resistance R does not affect the null point reading.
c) By increasing the length of the potentiometer the sensitivity can be increased.