Capacitance of an oil drop of radius r is C=4πεr when n drops combine to form a large drop of radius R, then n× volume of 1 small drop = volume of 1 large drop n×‌
4
3
πr3=‌
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πR3⇒R=n1∕3⋅r So, capacitance of large drop is C′=4πεR=4πε⋅n‌