Question

Circuit diagram of metre bridge is shown in figure. The null point is found at a distance of $40\, cm$ from $A$. If now a resistance of $12\, \Omega$ is connected in parallel with $S$, the null point occurs at $64\, cm$. Determine the value of $R$ and $S$.

• A. $\frac{40}{3} \Omega,\, 20\, \Omega$
• B. $\frac{10}{3} \Omega,\, 10\, \Omega$
• C. $11\, \Omega,\, 22\, \Omega$
• D. $\frac{80}{3} \Omega,\, 40\, \Omega$

Answer 1

Answer: (A)

$\frac{40}{60}=\frac{ R }{ S }$
$\frac{2}{3}=\frac{ R }{ S }$ ...(1)
$\frac{64}{36}=\frac{ R (12+ S )}{12 S }$
$\frac{16}{9}=\frac{ R (12+ S )}{12 S }$ ...(2)
$(1) /(2)$
$S =20 \Omega, R =\frac{40}{3} \Omega$