An ideal battery of 4 V and resistance R are connected in series in the primary circuit of a potentiometer of length 1 m and resistance 5 Ω. The value of R, to give a potential difference of 5 mV across 10 cm of potentiometer wire, is: (a) 480 Ω (b) 495 Ω (c) 490 Ω (d) 395 Ω

Answer: (d). k = (5 mV)/(10 cm) = 0.05 V/m, so p.d. across 1 m wire = 0.05 V. I = 0.05/5 = 0.01 A. Total resistance = 4/0.01 = 400 Ω, so R = 400 - 5 = 395 Ω. So the answer is (d) 395 Ω.

An ideal battery of 4 V and resistance R are connected in series in… | JEE Main 2019 (12 Jan, Shift 1)

Q70JEE Main 2019 · 12 JAN · SHIFT 1Medium

Potentiometer

An ideal battery of 4 V and resistance R are connected in series in the primary circuit of a potentiometer of length 1 m and resistance 5 $\Omega$ . The value of R, to give a potential difference of 5 mV across 10 cm of potentiometer wire, is:

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Answer: (d)

$k = \frac{5\ \text{mV}}{10\ \text{cm}} = 0.05\ \text{V/m}$ , so p.d. across 1 m wire $= 0.05\ \text{V}$ .
$I = \frac{0.05}{5} = 0.01\ \text{A}$ .
Total resistance $= \frac{4}{0.01} = 400\ \Omega$ , so $R = 400 - 5 = 395\ \Omega$ .
So the answer is (d) $395\ \Omega$ .

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Potentiometer question from JEE Main 2019 (12 Jan, Shift 1)

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