Question

In potentiometer experiment, null point is obtained at a particular point for a cell on potentiometer wire x cm long. If the length of the potentiometer wire is increased without changing the cell, the balancing length will (Driving source is not changed)

• A. increase
• B. decrease
• C. not change
• D. becomes zero

Answer 1

The correct option is A increase

Let driving source $=V$, Resistance and length of potentiometer wire $=R$ and $L_1$, Balancing length $=l_1$, cell voltage $=E$

So at balancing point-

$\frac{E}{V}=\frac{l_1}{L_1}$

After changing length of potentiometer wire $=L_2$, balancing length $=l_2$

Now $\frac{E}{V}=\frac{l_2}{L_2}$

By solving

$l_2=l_1\left(\frac{L_2}{L_1}\right)$

As $L_2>L_1⟹l_2>l_1$