Question

Shown in the figure is a meter-bridge set up with null deflection in the galvanometer. The value of the unknown resistance R is?

• A. $55\Omega$
• B. $13.75\Omega$
• C. $220\Omega$
• D. $110\Omega$

Answer 1

The correct option is C $220\Omega$

This is a Wheatstone bridge.
If ${\rho }_l$ is the resistance per unit length (in cm)
$\frac{20{\rho }_l}{55}=\frac{80{\rho }_l}{R}$
or $R=\frac{80\times 55}{20}=220\Omega$.