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Question: Answered & Verified by Expert
In a cylinder-piston arrangement, the air is under a pressure P1. A soap bubble of radius r lies inside the cylinder. Soap bubble has surface tension T. The radius of soap bubble is to be reduced to half. Find the pressure P2 to which air should be compressed isothermally.
PhysicsMechanical Properties of FluidsJEE Main
Options:
  • A P 1 + 4 T r
  • B 4 P 1 + 1 2 T r
  • C 8 P 1 + 2 4 T r
  • D P 1 + 2 T r
Solution:
2754 Upvotes Verified Answer
The correct answer is: 8 P 1 + 2 4 T r
Using PiVi = Pf Vf  (for the air bubble)

we have

P 1 + 4 T r 4 3 π r 3 = P 2 + 4 T r / 2 4 3 π r 2 3

Solving this, we get

P 2 = 8 P 1 + 2 4 T r

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