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)

Hint: The potential drop across a piece of uniform cross-section wire carrying a constant current is directly proportionate to its length, according to the principle of a potentiometer.

Explanation:

Step 1: Concept used:

according to the principle of a potentiometer, the potential drop across a piece of uniform cross-section wire carrying a constant current is directly proportionate to its length.

Step Finding value of length by given condition:

Let driving source $=E_p$, Resistance and length of potentiometer wire $= R$ and $L$, Balancing length $=l$, cell voltage $= V$

So at balancing point-

$\dfrac{V}{E_p}=\dfrac{l}{L}$ ...........(1)

After changing length of potentiometer wire $=L_1$, balancing length $=l_1$

Now $\dfrac{V}{E_p}=\dfrac{l_1}{L_1}$ .........(2)

Step 3: Conclusion:

By solving both equations, we get:

$l_1= l(\dfrac{L_1}{L})$

As $L_1 >L \implies l_1>l$

Hence option A is correct.