Question

A galvanometer of resistance $2\Omega$ acts as a voltmeter of range 250 V with 5000$\Omega$ resistance in series. If same galvanometer is used as ammeter with $2\times {10}^{-3}\Omega$ shunt resistance, then range of such ammeter will be

• A. (0 - 5) A
• B. (0 - 50) A
• C. (0 - 100) A
• D. (0 - 25) A

Answer 1

The correct option is B (0 - 50) A

Say, $i_{max}$ is the maximum current the galvanometer can take.
$250=i_{max}(2+5000)\Rightarrow i_{max}\approx 5\times {10}^{-2}A$
In the second case, when the current in the galvanometer is $i_{max},$ the current in the shunt resistance is $\frac{2}{2\times {10}^{-3}}\times i_{max}=50A$.
Threfore, the maximum current that the galvanometer can detect is $50+(5\times {10}^{-2})\approx 50A.$