WBJEE '13 Fluids Q

1 Answers

Soumyadeep Basu ·

Excess pressure inside a soap bubble is 4TR. As surface tension for both the bubbles is the same, pressure inside the smaller bubble is greater than that inside the larger bubble (due to the smaller radius). So air will flow from the smaller bubble to the larger bubble. So (D) is the correct answer.

  • Aditya Agarwal But air will flow till pressure diff. = 0. so it will flow till r1=r2. Where am i going wrong.?
  • Akash Anand @Aditya..what is the logic behind your argument?
  • Aditya Agarwal Sir, i mean the pressure inside the smaller bubble is more. so air has to flow out from it. But if the answer is D, then the pressure inside the smaller bubble will increase further. Since Excess Pressure=4T/r. and r is decreasing. So the radii of the 2 bubbles should be equal at equilibrium. So where am i going wrong?
  • Soumyadeep Basu @Aditya, ultimately the pressure inside the bubble depends on the air inside it. 4T/R is just the expression for the excess pressure at equilibrium. As the radius of the bubble is changing, the bubble-air interface is obviously not in equilibrium.

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