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 Ω /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) 0.25 V (b) 0.20 V (c) 0.50V (d) 0.75 V

Answer: (a). Cells in series: emf = 3 V, internal resistance = 1 Ω. Wire resistance = 400 × 0.01 = 4 Ω; total R = 4 + 1 + 1 = 6 Ω. I = 3/6 = 0.5 A. Resistance of AJ = 50 × 0.01 = 0.5 Ω, so V = 0.5 × 0.5 = 0.25 V. So the answer is (a) 0.25 V.

In the circuit shown, a four-wire potentiometer is made of a 400 cm… | JEE Main 2019 (8 Apr, Shift 2)

Q74JEE Main 2019 · 8 APR · SHIFT 2Difficult

Potentiometer

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 :-

Show answer and solution

Answer: (a)

Cells in series: emf $= 3\ \text{V}$ , internal resistance $= 1\ \Omega$ .
Wire resistance $= 400 \times 0.01 = 4\ \Omega$ ; total $R = 4 + 1 + 1 = 6\ \Omega$ .
$I = \frac{3}{6} = 0.5\ \text{A}$ .
Resistance of AJ $= 50 \times 0.01 = 0.5\ \Omega$ , so $V = 0.5 \times 0.5 = 0.25\ \text{V}$ .
So the answer is (a) 0.25 V.

Report a mistake

Potentiometer question from JEE Main 2019 (8 Apr, Shift 2)

More questions on Potentiometer