Question

A moving coil galvanometer is converted into an ammeter reading up to $0.03 \,A$ by connecting a shunt of resistance $4r$ across it. and into an ammeter reading up to $0.06 \,A$ when a shunt of resistance $r$ is connected across it. What is the maximum current which can be sent through this galvanometer if no shunt is used?

• A. 0.01 A
• B. 0.02 A
• C. 0.03 A
• D. 0.04 A

Answer 1

Answer: (B)

For an ammeter $\frac{i_{g}}{i}=\frac{S}{G+S}$
$\Rightarrow i_{g} G=\left(i-i_{g}\right) S$
$\therefore i_{g} G=\left(0.03-i_{g}\right) 4 r \ldots$ (i)
and $i_{g} G=\left(0.06-i_{g}\right) r \ldots$ (ii)
From Eqs. (i) and (ii)
$0.12-4 i_{g}=0.06-i_{g}$
$\Rightarrow i_{g}=0.02\, A$