A soap bubble is being blown at the end of a very narrow tube of radius b. Air (density ρ) moves with a velocity ‘v’ inside the tube and comes to rest inside the bubble. The surface tension of the soap solution is T. After some time the bubble, having grown to a radius ‘r’, separates from the tube. Find the value of ‘r’. Assume that r>>b so that you can consider the air to be falling normally on the bubble’s surface.

Question

Infinity Learn · Accepted Answer

The bubble will separate from the tube when thrust force exerted by the air is equal to the force due to excess pressure. i.e. ρ$$Av2=4TrA$$  or  $$r=4T$$ρ$$v2$$

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