Question

In a potentiometer the null point is obtained at $7^\text{th}$ wire. If now we have to change the null point at $9^\text{th}$ wire, what should we do?

• A. Attach resistance in series with battery
• B. Increase resistance in main circuit
• C. Decrease resistance in main circuit
• D. Decrease applied emf

Answer 1

Answer: (B)

Increase resistance in main circuit

Answer 2

The working of potentiometer is based on the fact that the fall of potential across any portion of the wire is directly proportional to the length of that portion provided the wire is of uniform area of cross-section and a constant current is flowing through it. To shift the balance point on higher length, the potential gradient of the wire is to be decreased. The same can be obtained by decreasing the current of the main circuit, which is possible by increasing the resistance in series of potentiometer wire.