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MHT CET202617 April 2026Morning ShiftPhysicsMechanical Properties of FluidsActual

A soap bubble of radius 1 cm is expanded to radius 3 cm. Surface tension of soap solution is 25 dyne/cm. The work done during expansion in erg is

Options

  1. A800
  2. B1200
  3. C1600
  4. D2400

Correct answer

C. 1600

Step-by-step solution

Work done in expanding a soap bubble is given by W = T A Since a soap bubble has two free surfaces, the change in surface area is A = 2 4 (R₂^2 - R₁^2) Given R₁ = 1 cm and R₂ = 3 cm A = 8 ( ( 3 )^2 - ( 1 )^2 ) A = 8 ( 9 - 1 ) = 8 8 = 64 cm ^2 Given surface tension T = 25 dyne/cm W = 25 64 = 1600 erg Answer: 1600

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