Question

State the working principle of potentiometer explain with the help of circuit diagram. How the emf of two primary cells are compared by using the potentiometer.

Answer 1

The principle of potentiometer:

The potential drop along any length of the wire is directly proportional to that length. When a constant current flows through a wire of uniform cross section and composition then, $v\alpha 1$

When the key $K$ is closed, a constant current flows through the potentiometer wire. By closing key $K_1$, the null point can be obtained by cell $E_1$. The jockey is moved along the wire and adjusted still galvanometer shoes no deflection.

Suppose, $A{J}_1=l_1$ is the balancing length for cell $E_1$.

Then $E_1=k{l}_2$ where $k\to$ Potential gradient

Now, let the null point of cell $E_2$ be obtained by closing key $K_2$

Let $A{J}_2=l_2$

Then, $E_2=K{l}_2$

$\therefore \frac{E_2}{E_1}=\frac{I_2}{I_1}$

Hence, by increasing a length of a potentiometer's wire, the sensitivity of a potentiometer can be increased.