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  • An ammeter is obtained by shunting a 30  galvanometer with a 30 <img alt="\Omega" src="http://entran

An ammeter is obtained by shunting a 30 \Omega galvanometer with a 30 \Omega resistance. What additional shunt (in \Omega ) should be connected across it to double the range?

Option: 1

15


Option: 2

10


Option: 3

5


Option: 4

0


Answers (1)

best_answer

\begin{aligned} &\text { Initially, } \mathrm{S}=\frac{\mathrm{i}_{\mathrm{g}}}{\mathrm{I}-\mathrm{i}_{\mathrm{g}}} \mathrm{G}\\ &30=\frac{\mathrm{i}_{\mathrm{g}}}{\mathrm{I}-\mathrm{i}_{\mathrm{g}}} \times 30 \Rightarrow \mathrm{I}=2 \mathrm{i}_{\mathrm{g}}\\ &\text { When range is doubled i.e I }^{\prime}=2 \mathrm{I}=4 \mathrm{i}_{\mathrm{g}}\\ &\text { Now shunt required is: } \mathrm{S}^{\prime}=\frac{\mathrm{i}_{\mathrm{g}}}{\mathrm{I}^{\prime}-\mathrm{i}_{\mathrm{g}}} \mathrm{G}=\frac{\mathrm{i}_{\mathrm{g}}}{4 \mathrm{i}_{\mathrm{g}}-\mathrm{i}_{\mathrm{g}}} \times 30=10 \Omega\\ &\text { As shunt is connected in parallel to galvanometer, if additional shunt } x \text { then }\\ &30 \| \mathrm{x}=10 \text { or } \frac{30 \mathrm{x}}{30+\mathrm{x}}=10\\ &30+\mathrm{x}=3 \mathrm{x} \Rightarrow \mathrm{x}=15 \Omega \end{aligned}

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