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Twenty-seven drops of the same size are charged at 220 V each. They combine to form a bigger drop. Calculate the potential of the bigger drop.

1. 660 V
2. 1320 V
3. 1520 V
4. 1980 V

Correct answer: 1320 V

Solution

For a charged conducting sphere, potential is proportional to \(Q/R\). When 27 identical drops combine, total charge becomes 27 times and radius becomes \(27^{1/3}=3\) times, so the potential becomes \(27/3=9\) times the original.

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