Question

In the circuit $P\ne R$,

the reading of the galvanometer is same with switch $S$ open or closed. Then

• A. $I_R=I_G$
• B. $I_P=I_G$
• C. $I_Q=I_G$
• D. $I_Q=I_R$

Answer 1

Answer: (A)

This method is Kelvin's method of determining resistance of galvanometer by Wheatstone bridge circuit. Deflection in galvanometer $G$ is same with switch $S$ open or closed. It means that there is no current through $S$. This happens when the potentials at the two ends of $S$ are same.
This is the condition of balanced Wheatstone bridge.
$\therefore I_P=I_Q$ and $I_R=I_G$.