Question

In a metre bridge, the gaps are closed by two resistances P & Q & the balance point is obtained at 40 cm. when Q is shunted by a resistance of $10\Omega$, the balance point shifts to 50 cm. the values of P & Q are

respectively

• A.
• B. 20Ω, 30Ω
• C. 10Ω, 15Ω
• D. 5Ω, 10Ω

Answer 1

The correct option is A

$R=\frac{Sl}{(100-l)}\Rightarrow P=\frac{Q\times 40}{60}=\frac{2}{3}Q$

when Q is shunted with $10\Omega$

$Q‘=\frac{10Q}{10+Q‘}I=50cm\therefore P=\frac{10Q}{10+Q}\times \frac{50}{50}=\frac{10Q}{10+Q}$

$\frac{2}{3}Q=\frac{10Q}{10+Q}\Rightarrow Q=5\Omega$

$\therefore P=\frac{10}{3}\Omega$