Question

Two students ‘X’ and ‘Y’ perform an experiment on potentiometer separately using the circuit given below:

Keeping other parameters unchanged, how will the position of the null point be affected if

(i) ‘X’ increases the value of resistance R in the set-up by keeping the key K₁ closed and the Key K₂ opens?

(ii) ‘Y’ decreases the value of resistance S in the set-up, while the key K₂ remains open and they K₁ closed?

Justify.

Answer 1

(i) K₁→ closed, K₂→ Open

Suppose null point occurs at l,

Apply KVL in smaller loop,

ξ − l∅ = 0 …..(1)

Where, ∅ = potential drop per unit length in potentiometer wire

ξ = l∅

`=> l =xi/phi`

As X increase the value of resistance R, So, current in the circuit (wire) decrease. Hence, ∅ will be increases. Then l will decrease.

We can say, as X increases the value of R, null point decrease.

(ii) K2 → open, K1 → closed.

Then the circuit will be same as shown earlier.

We see that resistance S is not involved in the circuit because K₂ is open.

So, from equation (1)

ξ = ∅l

`=> l=xi/phi`

Here, ∅ does not depends on the value of resistance S.

So, ∅ null point is not affected by decreasing the value of resistance S.