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A liquid drop has two principal radii of curvature R1 = 1 m and R2 = 2 m in two mutually perpendicular planes. Taking surface tension S = 0.07 N/m, the excess pressure inside the drop is _____.
- 0.07 N/m²
- 0.105 N/m²
- 0.035 N/m²
- None of these
Correct answer: 0.105 N/m²
Solution
For a curved liquid surface, the Young-Laplace equation gives excess pressure = S(1/R1 + 1/R2). With S = 0.07, R1 = 1 m, R2 = 2 m: excess = 0.07 * (1 + 1/2) = 0.07 * 1.5 = 0.105 N/m².
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