Question
An ammeter whose resistance is $180\,\Omega $ gives full scale deflection when current is $2\, mA$. The shunt required to convert it into an ammeter reading $20\, mA$ (in $ohms$) is
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Answer
(b) Given ${i_g} = 2\,mA,$ $i = 20\,mA,\,G = 180\,\Omega $
$\frac{{{i_g}}}{i} = \frac{S}{{G + S}}$
$ \Rightarrow $ $180 + S = 10S$
$ \Rightarrow $ $S = \frac{{180}}{9} = 20\,\Omega $
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