Sensitivity of a potentiometer can be increased by
(A). Increasing the emf of the cell
(B). Increasing the length of the potentiometer
(C). Decreasing the length of the potentiometer wire
(D). None of the above

Hint – In this question use the concept that a potentiometer is used to measure the potential difference/ electromotive force across certain length of a wire and has many other applications as well so sensitivity of a potentiometer is defined as the smallest potential difference that can be measured using the potentiometer. Consider the facts that influence this measurement. It will help approaching the problem.

Complete step-by-step solution -
Potentiometer is defined as an instrument which is used for measuring an electromotive force (emf).
It is done by balancing emf against the potential difference that is produced by passing a known amount of current.
Sensitivity of a potentiometer: Sensitivity of a potentiometer is the measure of the degree of the smallest potential difference it can measure (i.e. measured by using the potentiometer).
Now as we know that the sensitivity of the potentiometer is increased by decreasing the potential gradient and thereby increasing the resistivity of the potentiometer this is done by two methods which are given below:
$\left( a \right)$ Increasing the length of the potentiometer wire – by increasing the length of the potentiometer wire sensitivity of the potentiometer is increased because as the length of the potentiometer is increased we can measure much smallest potential difference as compare to previous one so the sensitivity is increased.
$\left( b \right)$ By reducing the current in the circuit by using a rheostat (it is a variable resistor with a sliding contact by adjusting the sliding contact of the rheostat we can change the value of the resistor).
So this is the required answer.
Hence option (B) is the correct answer.

Note – Potentiometer has a vivid number of applications it can be used to calculate the internal resistance of the cell, even to compare the different emf’s of cells moreover the very popular use of potentiometer is that it is used as a variable resistor in many devices.