Question

A resistance of $2\Omega$ is connected across one gap of a metre–bridge (the length of the wire is 100 cm) and an unknown resistance, greater than $2\Omega$, is connected across the other gap. When these resistances are interchanged, the balance point shifts by 20 cm. Neglecting any corrections, the unknown resistance is

• A. $3\Omega$
• B. $4\Omega$
• C. $5\Omega$
• D. $6\Omega$

Answer 1

The correct option is A $3\Omega$

$\frac{2\Omega }{R}=\frac{1}{100-1}$
$\frac{R}{2\Omega }=\frac{1+20}{100-1-20}\Rightarrow R=3\Omega$