Question

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 :

• A. 0.20 V
• B. 0.25 V
• C. 0.75 V
• D. 0.50V

Answer 1

Answer: (B)

0.25 V

Answer 2

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