Question

A galvanometer of resistance $ 20\Omega $ shows a deflection of $ 10 $ divisions when a current of $ 1\, mA $ is passed through it. If a shunt of $ 4\,\Omega $ is connected and there are $ 50 $ divisions on the scale, the range of the galvanometer is

• A. 1 A
• B. 3 A
• C. 10 mA
• D. 30 A
• E. 30 mA

Answer 1

Answer: (E)

Current for 50 divisions,
$ {{I}_{g}}=\frac{1\times 50}{10}=5\,mA $
$ \therefore $ $ \frac{{{I}_{g}}}{I}=\frac{S}{S+G} $
$ \Rightarrow $ $ I=\left( \frac{S+G}{S} \right){{I}_{g}} $
Or $ I=\left( \frac{4+20}{4} \right)5mA $
$ =30\,mA $