Question

A galvanometer of resistance $100\Omega$ gives a full scale deflection for a current of ${10}^{-5}A$. To convert it into a ammeter capable of measuring upto $1A,$ we should connect a resistance of

• A. $1\Omega$ in parallel
• B. ${10}^{-3}\Omega$ in parallel
• C. ${10}^5\Omega$ in parallel
• D. $100\Omega$ in parallel

Answer 1

Answer: (B)

${10}^{-3}\Omega$ in parallel

Here, $R_g=100\Omega ;I_g={10}^{-5}A;I=1A;$

$S=\frac{I_g{R}_g}{I-I_g}=\frac{{10}^{-5}\times 100}{1-{10}^{-5}}$
$\approx {10}^{-3}\Omega$ in parallel