Question

A moving coil galvanometer is converted into an ammeter reading upto 0.03 A by connecting a shunt of resistance 4r across it and into an ammeter reading upto 0.06 A when a shunt of resistance r 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

The correct option is B 0.02 A

For ammeter, $S=\frac{i_g}{(i-i_g)}G\Rightarrow i_{g}G=(i-i_g)S$
So $i_{g}G=(0.03-i_g)4r$ .........(i) and $i_{g}G=(0.06-i_g)r$
Dividing equation (i) by (ii) $1=\frac{(0.03-i_g)4}{0.06-i_g}\Rightarrow 0.06-i_g=0.12-4i_g$
$\Rightarrow 3i_g=0.06\Rightarrow i_g=0.02A$