Physics - Current Electricity Question with Solution | TestHub

In an ammeter, the galvanometer of resistance $G$ and the shunt resistance $S$ are connected in parallel.

The current through the galvanometer is given by $I_g=I\left(\frac{S}{G+S}\right)$.

Given that $I_g=0.25\%\text{ of }I=\frac{0.25}{100}I=\frac{1}{400}I$.

Therefore, $\frac{S}{G+S}=\frac{1}{400}$.

The equivalent resistance of the ammeter is $R_A=\frac{GS}{G+S}$.

Substituting the ratio, we get:

$R_A=G\left(\frac{S}{G+S}\right)=G\left(\frac{1}{400}\right)=\frac{1}{400}G$.

Answer: $\frac{1}{400}\mathrm{G}$