Three resistances, P, Q, R each of 2 Ω and an unknown resistance S from the four arms of a Wheatstone bridge circuit. When a resistance of 6 Ω is connected in parallel to S the bridge gets balanced. What is the value of S? (a) 3 Ω (b) 6 Ω (c) 1 Ω (d) 2 Ω.

Answer: (a). P = Q = R = 2 Ω, so balance needs the fourth arm = 2 Ω. 6S/S+6 = 2 ⇒ 6S = 2S + 12 S = 3 Ω So the answer is (a) 3 Ω.

Three resistances, P, Q, R each of 2 Ω and an unknown resistance S… | NEET 2007 (AIPMT)

Q82NEET 2007 · AIPMTMedium

Wheatstone Bridge & Metre Bridge

Three resistances, P, Q, R each of 2 $\Omega$ and an unknown resistance S from the four arms of a Wheatstone bridge circuit. When a resistance of 6 $\Omega$ is connected in parallel to S the bridge gets balanced. What is the value of S?

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Answer: (a)

$P = Q = R = 2\ \Omega$ , so balance needs the fourth arm $= 2\ \Omega$ .
$\dfrac{6S}{S+6} = 2 \Rightarrow 6S = 2S + 12$
$S = 3\ \Omega$
So the answer is (a) $3\ \Omega$ .

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