question_answer

In the circuit shown, a four-wire potentiometer is made of a 400 cm long wire, which extends between A and B. The resistance per unit length of the potentiometer wire is \[r=0.01\Omega /cm.\]. If an ideal voltmeter is connected as shown with jockey J at 50 cm from end A, the expected reading of the voltmeter will be :-             [JEE Main 8-4-2019 Afternoon]

A) 0.20 V             

B) 0.25 V

C) 0.75 V

D)   0.50V

Correct Answer: B

Solution :

Resistance of wire \[AB=400\times 0.01=4\Omega \]\[i=\frac{3}{6}=0.5A\] Now voltmeter reading = i (Resistance of 50 cm length) \[=\left( 0.5A \right)\left( 0.01\times 50 \right)=0.25\] volt