Current Electricity 4 Question 27
27. A galvanometer gives full scale deflection with 0.006 A current. By connecting it to a $4990 \Omega$ resistance, it can be converted into a voltmeter of range $0-30 V$. If connected to a $\frac{2 n}{249} \Omega$ resistance, it becomes an ammeter of range $0-1.5 A$. The value of $n$ is
(2014 Adv.)
Analytical & Descriptive Questions
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Solution:
$i _g(G+4990)=V$
$$ \begin{aligned} & \Rightarrow \quad \frac{6}{1000}(G+4990)=30 \\ & \Rightarrow \quad G+4990=\frac{30000}{6}=5000 \\ & \Rightarrow \quad G=10 \Omega \\ & V _{a b}=V _{c d} \\ & \Rightarrow \quad i _g G=\left(1.5-i _g\right) S \\ & \Rightarrow \quad \frac{6}{1000} \times 10=1.5-\frac{6}{1000} S \\ & \Rightarrow \quad S=\frac{60}{1494}=\frac{2 n}{249} \\ & \Rightarrow \quad n=\frac{249 \times 30}{1494}=\frac{2490}{498}=5 \end{aligned} $$
