Question:
A soap bubble of surface tension 30 *10-3 N has radius 2 cm. What is the work done in doubbling the radius ?
Answer:
Surface tension T = 30 * 10-3 N
Surface area of spherical bubble S1 = 4 ∏ r2 = 4 * 22/7 * 2 * 10-2 * 2 * 10-2 = 50.24 * 10-4
S2 = 4 ∏ (2r)2 = 4S1
Work done = T (S2 – S1) = 30 * 10-3 * (4S1 – S1) = 30 * 10-3 * 3 * 50.24 * 10-4 = 4521.6 * 10-7 J
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