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

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Correct Answer

(D) \(1.25 \times {10^{ - 2}}\,\Omega \)

Detailed explanation

A ccording to question, current through galvanometer, \(\mathrm{I}_{\mathrm{g}}=1\, \mathrm{mA}\)

Current through shunt \(\left(I-I_{g}\right)=2\, A\)

Galvanometer resistance \(\mathrm{R}_{\mathrm{g}}=25\, \Omega\)

Resistance of shunt, \(\mathrm{S}=?\)

\(\mathrm{I}_{\mathrm{g}} \mathrm{R}_{\mathrm{g}}=\left(\mathrm{I}-\mathrm{I}_{\mathrm{g}}\right) \mathrm{S}\)

\( \Rightarrow S = \frac{{{{10}^{ - 3}} \times 25}}{2}\)

\(S \simeq 1.25 \times {10^{ - 2}}\,\Omega \)

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