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JEE Main 2019 (11 Jan, Shift 1) · Wheatstone Bridge & Metre Bridge

Wheatstone Bridge & Metre Bridge question from JEE Main 2019 (11 Jan, Shift 1)

Q65JEE Main 2019 · 11 JAN · SHIFT 1Medium

Wheatstone Bridge & Metre Bridge

In a Wheatstone bridge(see fig.), Resistances P and Q are approximately equal. When R = 400 $\Omega$ , the bridge is balanced. On interchanging P and Q, the value of R, for balance, is 405 $\Omega$ . The value of X is close to:

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Answer: (a)

First balance: $\dfrac{P}{Q} = \dfrac{400}{X}$ (R and X opposite P, Q).
After interchange: $\dfrac{Q}{P} = \dfrac{405}{X}$
Multiply: $1 = \dfrac{400 \times 405}{X^2} \Rightarrow X = \sqrt{400 \times 405}$
$X \approx 402.5\ \Omega$
So the answer is (a) $402.5$ ohm.

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