Potentiometer has multiple uses. It is based on the principle that when constant current flows through a wire of uniform area of cross-section then potential drop along its length is directly proportional to corresponding length.

i.e.  $V \propto I$

$V=K I$

Various uses of potentiometer on:

• To measure potential differences between any two points in an electrical network
• To compare emf of a cell
• To measure emf of a cell
• To measure internal resistance of a cell etc.

Answer the following question related to potentiometer:

The length of potentiometer wire AB is 10 m and its resistance is 8Ω. If balancing length on the potentiometer is 225 cm, the value of emf of the primary cell is:

0.36 volt

The correct answer is Option (1) → 0.36 volt

Potential gradient per unit length = $\frac{i × R_{A B}}{l}$

$\Rightarrow v=\frac{2}{2+8} × \frac{8}{10}=\frac{1}{5} × \frac{8}{10}$

Now, emf of primary cell = Potential gradient × Balancing length

$=\frac{1}{5} × \frac{8}{10} × \frac{225}{100}$ = 0.36 volt