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  4. A galvanometer of 25 ohms and having full scale deflection for a current of 10 mA is changed into voltmeter of range 100 volts by connecting a resistance R in series with the galvanometer. The resistance R in ohms is:

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Q. A galvanometer of 25 ohms and having full scale deflection for a current of 10 mA is changed into voltmeter of range 100 volts by connecting a resistance R in series with the galvanometer. The resistance R in ohms is:

JIPMERJIPMER 1996

Solution:

Using formula for resistance R $ R=\frac{V}{{{i}_{g}}}-G $ Here, $ G=25\,\Omega , $ $ {{i}_{g}}=10\times {{10}^{-3}}A, $ $ V=100\,V $ On putting the value in above formula, we get $ =\frac{100}{10\times {{10}^{-3}}}-25 $ $ =1000-25 $ $ =9975\,ohm $