Question

The value of unknown resistance $X$ will be

• A. $402.49\Omega$
• B. $403\Omega$
• C. $404\Omega$
• D. $210\Omega$

Answer 1

Answer: (D)

$210\Omega$

Initially when bridge gets balanced the balancing condition is given by

$\frac{P}{Q}=\frac{R}{X}$

$\frac{P}{Q}=\frac{100}{X}$......................................$\left(1\right)$

When $P$ and $Q$ are mutually interchanged then the bridge gets

balanced again and the balancing condition is given by

$\frac{Q}{P}=\frac{R}{X}$

$\frac{Q}{P}=\frac{441}{X}$

From$\left(1\right),$ we can write,

$\frac{441}{X}=\frac{X}{100}$

$X^2=441\times 100$

$X^2=44100$

$X=210\Omega$