Question

For a post office box, the graph of galvanometer deflection versus (resistance pulled out of resistance box) for the ratio $100:1$ is given as shown. Find the value of unknown resistance.

Answer 1

For post office box (wheat stone Bridge)

under balanced condition.

$\frac{P}{Q}=\frac{R}{S}$, where $S$ is unknown resistance

$S=\frac{Q}{P}\times R$ [$\because P/Q=100$]

From the given graph, the galvanometer shown $\lambda$ zero deflection at $R=323.75\approx 324\Omega$

So, $S=3.24\Omega$