A galvanometer with its coil resistance 25  Ω requires a current of 1   mA for its full…

1. $1.25 \times {10}^{-\mathrm{2 }}\mathrm{\Omega }$
2. $2.5 \times {10}^{-\mathrm{3 }}\mathrm{\Omega }$
3. $2.5 \times {10}^{-\mathrm{2 }}\mathrm{\Omega }$
4. $1.25 \times {10}^{-\mathrm{3 }}\mathrm{\Omega }$

Solution

From the above figure, it is clear that, $I_g{R}_g=(I- I_g)S$
$S \simeq \frac{{10}^{-3}\times 25}{2}$$\Rightarrow S \simeq 12.5 \times {10}^{-3}$
$\Rightarrow 1.25 \times {10}^{-2}\mathrm{\Omega }$

Asked in: JEE Main 2018 (16 Apr Online)

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