Question

In Wheatstone's bridge P=9ohm, Q=11ohm, R=4ohm and S=6ohm. How much resistance must be put in parallel to the resistance S to balance the bridge

• A. 24 ohm
• B. $\frac{44}{9}$ ohm
• C. 26.4 ohm
• D. 18.7 ohm

Answer 1

The correct option is C 26.4 ohm

$\frac{P}{Q}=\frac{R}{S^{\prime }}$ (For balancing bridge)
$\Rightarrow S^{\prime }=\frac{4\times 11}{9}=\frac{44}{9}$
$\Rightarrow \frac{1}{S^{\prime }}=\frac{1}{r}+\frac{1}{6}$
$\Rightarrow \frac{9}{44}-\frac{1}{6}=\frac{1}{r}$
$\Rightarrow r=\frac{132}{5}=26.4\Omega$