State underlying principle of a potentiometer

State the underlying principle of a potentiometer. Write two factors on which the sensitivity of a potentiometer depends.

In the potentiometer circuit shown in the figure, the balance point is at X. State, giving reason, how the balance point is shifted, when:
(i) resistance R is increased ?
(ii) resistance S is increased, keeping R constant ?

Principle of potentiometer: Fall of potential across any portion of a wire is directly proprotional to the length of that portion provided the wire is of uniform area of cross-section and current passing through it is constant.
${{E}{1}}$ / ${{E}{2}}$ = ${{l}{1}}$ / ${{l}{2}}$
There are two factors on which the sensitiviy of a potentiometer depends, i.e.,
(a) length of potentiometer (l)
(b) potential drop (E)
(i) If R increases, the potential gradient V/l decreases.
(ii) If S increases the potential difference increases.