Two students X and Y experiment potentiometer separately using the circuit diagram here. Keeping other things unchanged (i) X increases the value of resistance R (ii) Y decreases the value of resistance S in the setup. How will these changes affect the position of the null point in each case and why?

(i) For student A the null point shifts towards the right end B.

We know,

Where,

L = length of the potentiometer.

V = voltage across the potentiometer.

R = resistance of the potentiometer.

I = current flowing through the circuit.

l = length at which the emf e gets balanced

k = potential gradient

As the value of R increases the current from the driver cell decreases. This decreases the potential gradient (k). Hence a greater length is needed for balancing the same emf

(ii) For the student Y the null point shifts towards the left end A.

As the value of R decreases the current from the driver cell increases. This in the potential gradient. Hence a shorter length is needed for balancing the same emf.