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  4. The resistance of a galvanometer coil is R, then the shunt resistance required to convert it into a ammeter of range 4 times, will be

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Q. The resistance of a galvanometer coil is $R$, then the shunt resistance required to convert it into a ammeter of range $4$ times, will be

Bihar CECEBihar CECE 2007Current Electricity

Solution:

Shunt is connected in parallel with galvanometer.
Ammeter is made by connecting a low resistance shunt $S$ in parallel with galvanometer $G$. Since $G$ and $S$ are in parallel, the potential difference across them is same
$ i_{g} \times G=\left(i-i_{g}\right) \times S$
Given, $G=R, i=4 i_{g}$
image
$\therefore S=\frac{i_{g}}{4 i_{g}-i_{g}} \times R=\frac{i_{g}}{3 i_{g}} \times R=\frac{R}{3}$
Note : Resistance of shunt is always low.