Moving Charges And Magnetism Ques 84
84. A galvanometer of $50 ohm$ resistance has 25 divisions. A current of $4 \times 10^{-4}$ ampere gives a deflection of one per division. To convert this galvanometer into a voltmeter having a range of 25 volts, it should be connected with a resistance of
[2004, 2002]
(a) $2450 \Omega$ in series
(b) $2500 \Omega$ in series.
(c) $245 \Omega$ in series.
(d) $2550 \Omega$ in series.
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Answer:
Correct Answer: 84.(a)
Solution:
- (a) $R_g=50 \Omega, I_g=25 \times 4 \times 10^{-A} \Omega=10^{-2} A$ Range of $V=25$ volts
$ \begin{aligned} & V=I_g(R_e+R_g) \\ & \therefore R_e=\frac{V}{I_g}-R_g=2450 \Omega \end{aligned} $
In order to increase the range of voltmeter $n$ times the value of resistance to be connected in series with galvanometer is
$ R=(n-1) G $
Here, $G=$ resistance of galvanometer
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