Question

In a meter bridge, the gaps are closed by two resistances P and Q and the balance point is obtained at 40 cm.When Q is shunted by a resistance of $15\Omega$, the balance point shifts to 66.67 cm. The values of P and Q are

• A. $20\Omega ,30\Omega$
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• B. $10\Omega ,15\Omega$
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• C. $5\Omega ,7.5\Omega$
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• D. $\frac{10}{3}\Omega ,5\Omega$
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Answer 1

The correct option is A $20\Omega ,30\Omega$

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$\frac{P}{Q}=\frac{40}{60}=\frac{2}{3}\to \left(1\right)\frac{P}{\left(\frac{15Q}{15+Q}\right)}=\frac{66.67}{100-66.67}=\frac{66.67}{33.33}=2\frac{P}{15Q}\times (15+Q)=2\frac{2\times (15+Q)}{15\times 3}=215+Q=45;Q=45-15P=20\Omega Q=30\Omega$