Question 363 of 380

A galvanometer with its coil resistance $25\Omega$ requires a current of $1mA$ for its full deflection. In order to construct an ammeter to read up to a current of $2A$ the approximate value of the shunt resistance should be:

A$1.25\times {10}^{-2}\Omega$B$2.5\times {10}^{-3}\Omega$C$2.5\times {10}^{-2}\Omega$D$1.25\times {10}^{-3}\Omega$

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Answer: (A) $1.25\times {10}^{-2}\Omega$

From the above figure, it is clear that, ${I}_{g}{R}_{g}=(I-{I}_{g})S$
$S≃\dfrac{{10}^{-3}\times 25}{2}$$\Rightarrow S≃12.5\times {10}^{-3}$
$\Rightarrow 1.25\times {10}^{-2}\Omega$