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A soap bubble is blown slowly at the end of a tube by a pump supplying air at a constant rate. Draw a graph to represent the variation between the excess pressure inside the bubble with time.

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Excess pressure inside a soap bubble is 4T/R. Since air is blown at constant rate dV/dt is known. From rate change of volume calculate rate change of radius. Hence you get excess pressure in terms of time by putting R as f(t) in the formula.

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    $\begingroup$ Will it be dv/Dt= 4 pi r^2 Dr/Dt , then I'll put the relation in p=4T/r is it correct $\endgroup$ – Shub Mar 9 '17 at 18:39
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    $\begingroup$ @PhysiBoy I think you need to use a constant mass rate rather than a volume rate? $\endgroup$ – Farcher Mar 9 '17 at 21:03
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    $\begingroup$ @Farcher Agreed, but it probably won't make a difference at these low pressures. $\endgroup$ – WetSavannaAnimal Mar 9 '17 at 23:52
  • $\begingroup$ Correct @WetSavannaAnimal $\endgroup$ – user147979 Mar 10 '17 at 3:36
  • $\begingroup$ Yes @Shub you are right $\endgroup$ – user147979 Mar 10 '17 at 3:41

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