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An ideal battery of 4 V and resistance R are connected in series in the primary circuit of a potentiometer of length 1 m and resistance 5 Ω . The value of R, to give a potential difference of 5 mV across 10 cm of potentiometer wire, is :

1. 480 Ω
2. 495 Ω
3. 490 Ω
4. 395 Ω

Correct answer: 395 Ω

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