Properties Of Solids And Liquids Question 310

Question: The pressure of air in a soap bubble of 0.7cm diameter is 8 mm of water above the pressure outside. The surface tension of the soap solution is [MP PET 1991; MP PMT 1997]

Options:

A) $ 100dyne/cm $

B) $ 68.66dyne/cm $

C) $ 137dyne/cm $

D)$ 150dyne/cm $

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Answer:

Correct Answer: B

Solution:

$ \Delta P=\frac{4T}{r}=hdg\Rightarrow T=\frac{rhdg}{4} $

$ =\frac{0.35\times 0.8\times 1\times 10^{3}}{4} $

$ =70\ dyne/cm $

$ \equiv 68.66\ dyne/cm $



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