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A galvanometer of resistance 50 Ω is connected to battery of 3V along with a resistance of 2950 Ω in series. A full scale deflection of 30 divisions is obtained in the galvanometer. In order to reduce this deflection to 20 divisions, the resistance in series should be

1. 5050 Ω
2. 5550 Ω
3. 6050 Ω
4. 4450 Ω

Correct answer: 5050 Ω

Solution

The deflection in a galvanometer is proportional to the current passing through it. To reduce the deflection from 30 to 20 divisions, the current must decrease by a factor of 2/3. Using Ohm's law and the concept of equivalent resistance, the new series resistance is calculated as 5050 Ω.

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