Magnetics Ques 130
- A moving coil galvanometer allows a full scale current of $10^{-4}$ $ A$. A series resistance of $2$ $M \Omega$ is required to convert the above galvanometer into a voltmeter of range $0-5$ $V$. Therefore, the value of shunt resistance required to convert the above galvanometer into an ammeter of range $0.10$ $mA$ is
(2019 Main, 10 April)
(a) $100$ $\Omega$
(b) $500$ $\Omega$
(c) $200$ $\Omega$
(d) $10$ $\Omega$
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Answer:
Correct Answer: 130.(*)
Solution:
Formula:
- Given data,
$ \begin{aligned} I & =10^{-4} A, \\ R _S & =2 m\Omega=2 \times 10^{-3} \Omega \\ V _{\max } & =5 V \end{aligned} $
Let the internal resistance of the galvanometer be $R_G$.
$ \begin{array}{lc} Then, & I \times R_S + I \times R_G = V_{\max} \ \Rightarrow & 2 \times 10^{6} \times 10^{-4}+10^{-4} \times R _G=5 \\ \Rightarrow & 10^{-4} R _G=5-200=-195 \\ \text { or } & R _G=-195 \times 10^{4} \Omega \end{array} $
Resistance cannot be negative.
$\therefore$ No option is correct
BETA
