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NEET 2013 · Wheatstone Bridge & Metre Bridge

Wheatstone Bridge & Metre Bridge question from NEET 2013

Q79NEET 2013Medium

Wheatstone Bridge & Metre Bridge

The resistances of the four arms P, Q, R and S in a Wheatstone's bridge are 10 ohm, 30 ohm, 30 ohm and 90 ohm, respectively. The e.m.f. and internal resistance of the cell are 7 volt and 5 ohm respectively. If the galvanometer resistance is 50 ohm, the current drawn from the cell will be

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Answer: (d)

$\dfrac{P}{Q} = \dfrac{10}{30} = \dfrac{1}{3} = \dfrac{R}{S} = \dfrac{30}{90}$ : balanced, so no current through the galvanometer.
$(P+Q) \parallel (R+S) = 40 \parallel 120 = 30\ \Omega$
$I = \dfrac{7}{30 + 5} = 0.2$ A
So the answer is (d) $0.2$ A.

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