Question

The length of a potentiometer wire is 1200 cm and it carries a current of 60 mA. For a cell of emf 5V and internal resistance of 20 Ω, the null point on it is found to be a 1000cm. The resistance of whole wire is :

(1) 120 Ω 

(2) 60 Ω

(3) 80 Ω

(4) 100 Ω

Answer 1

Answer is (4) 100 Ω

5 = λl

where λ is potential gradient & L is total length of wire.

R = 100 Ω

Answer 2

The correct answer is (4) 100 Ω