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A galvanometer of resistance 25 ohm shows full-scale deflection at a current of 10 mA. To convert it into a voltmeter reading up to 100 V, a resistance R is connected in series with the coil. Find R (in ohm).

1. 10000
2. 10025
3. 975
4. 9975

Correct answer: 9975

Solution

Total resistance needed = V/Ig = 100/0.01 = 10000 ohm; subtract the galvanometer's 25 ohm to get R = 9975 ohm.

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