A galvanmeter has a coil of resistance $200 \Omega$ with a full scale deflection at $20 \mu \mathrm{A}$. The value of resistance to be added to use it as an ammeter of range $(0-20) \mathrm{mA}$ is ;

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Aicharya · Accepted Answer

$\begin{aligned} & \mathrm{G}=200 \Omega \ & \mathrm{i}_{\mathrm{g}}=20 \mu \mathrm{A} \ & \mathrm{i}=\mathrm{i}_{\mathrm{g}}\left(\frac{\mathrm{G}}{\mathrm{S}}+1ight) \ & \Rightarrow 20 	imes 10^{-3}=20 	imes 10^{-6}\left(\frac{200}{\mathrm{~S}}+1ight) \ & \Rightarrow \frac{200}{\mathrm{~S}}=999 \ & \Rightarrow \mathrm{S} \approx 0.2 \Omega\end{aligned}$

A galvanmeter has a coil of resistance $200 \Omega$ with a full scale deflection at $20 \mu \mathrm{A}$. The…

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