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NEET 2015 (AIPMT, Cancelled Paper) · Potentiometer

Potentiometer question from NEET 2015 (AIPMT, Cancelled Paper)

Q80NEET 2015 · AIPMT · CANCELLED PAPERMedium

Potentiometer

A potentiometer wire has length 4 m and resistance 8 $\Omega$ . The resistance that must be connected in series with the wire and an accumulator of e.m.f. 2 V, so as to get a potential gradient 1 mV per cm on the wire is

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Answer: (c)

$k = 1\ \text{mV/cm} = 0.1\ \text{V/m}$ , p.d. across wire $= 0.1 \times 4 = 0.4\ \text{V}$ .
$I = \frac{0.4}{8} = 0.05\ \text{A}$ .
Total resistance $= \frac{2}{0.05} = 40\ \Omega$ , so series $R = 40 - 8 = 32\ \Omega$ .
So the answer is (c) $32\ \Omega$ .

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