Question

In a meter -bridge, the balancing length from the left end when standard resistance of $1$ is in right gap is found to be $20cm$. The value of unknown resistance is

• A. $0.25\Omega$
• B. $0.5\Omega$
• C. $0.4\Omega$
• D. $4\Omega$

Answer 1

The correct option is A $0.25\Omega$

Resistance in right gap $R=1\Omega$

Let the unknown resistance be $P$.

Balancing length $l=20cm$

Using Wheat-stone bridge equation, $\frac{P}{R}=\frac{l}{100-l}$

$\therefore$ $\frac{P}{1}=\frac{20}{100-20}$

OR $\frac{P}{1}=\frac{20}{80}$

$⟹$ $P=\frac{1}{4}=0.25\Omega$