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Work done in increasing the size of a soap bubble from a radius of 3 cm to 5 cm is nearly (surface tension of soap solution =0.03 N m⁻¹)

Asked in AIEEE 2011 · Work done on a soap bubble

• (1) 4π mJ
• (2) 0.2π mJ
• (3) 2π mJ
• (4) 0.4π mJ

Step-by-step solution

Why the other options are wrong

• (1) comes from no consistent slip lands here; it is ten times the key, while the two checkable wrong routes give 0.192π mJ (one surface only, option 2) and 1.54π mJ (diameters used as radii).
• (2) comes from counts only one surface: 4π T(r₂²-r₁²)=0.192π mJ, which rounds to 0.2π mJ. The bubble's film has two faces, and that is where the 8π comes from.
• (3) comes from a filler; reading 3 cm and 5 cm as diameters multiplies every radius by 2 and the answer by 4, giving 1.54π mJ, which is the nearest reachable value and is not 2π mJ.

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