question_answer

A galvanometer coil has a resistance of \[10\,\,\Omega \]and the meter shows full scale deflection for a current of 1 mA. The shunt resistance required to convert the galvanometer into an ammeter of range 0-100 mA is about

A)  \[10\,\,\Omega \]            

B)  \[1\,\,\Omega \]

C)  \[0.1\,\,\Omega \]           

D)  \[0.01\,\,\Omega \]

Correct Answer: C

Solution :

 Let shunt resistance be S. Voltage across shunt is Now, \[V=(I-{{I}_{g}}).\,\,S\] and \[{{I}_{g}}\,.\,{{R}_{G}}=(I-{{I}_{g}})\,.\,\,S\] \[\Rightarrow \] \[S=\frac{{{I}_{g}}{{R}_{G}}}{(I-{{I}_{g}})}\] \[=\frac{{{10}^{-3}}\times 10}{(100\times {{10}^{-3}}-1\times {{10}^{-3}})}\] \[=\frac{10}{99}=0.1\,\Omega \]