Moving Charges and Magnetism - Result Question 78

80. A galvanometer has a coil of resistance $100 ohm$ and gives a full-scale deflection for $30 mA$ current. It is to work as a voltmeter of 30 volt range, the resistance required to be added will be

(a) $900 \Omega$

(b) $1800 \Omega$

(c) $500 \Omega$

(d) $1000 \Omega$

[2010]

(a) $2.4 N$

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Answer:

Correct Answer: 80. (a)

Solution:

  1. (a) Let the resistance to be added be $R$, then $30=I_g(r+R)$

$ \begin{aligned} & \therefore \quad R=\frac{30}{I_g}-r=\frac{30}{30 \times 10^{-3}}-100 \\ & =1000-100=900 \Omega \end{aligned} $



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