Current Electricity

JEE Main level, single correct, medium

321 of 380

Question 321 of 380

A galvanmeter has a coil of resistance 200Ω200 \Omega with a full scale deflection at 20μA20 \mu \mathrm{A}. The value of resistance to be added to use it as an ammeter of range (0−20)mA(0-20) \mathrm{mA} is ;

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Answer: (B) 0.20Ω0.20 \Omega

G=200Ωig=20μAi=ig(GS+1)⇒20×10−3=20×10−6(200 S+1)⇒200 S=999⇒S≈0.2Ω\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\right) \\ & \Rightarrow 20 \times 10^{-3}=20 \times 10^{-6}\left(\frac{200}{\mathrm{~S}}+1\right) \\ & \Rightarrow \frac{200}{\mathrm{~S}}=999 \\ & \Rightarrow \mathrm{S} \approx 0.2 \Omega\end{aligned}

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