Properties Of Solids And Liquids Question 336

Question: The radius of a soap bubble is increased from $ \frac{1}{\sqrt{\pi }} $ cm to $ \frac{2}{\sqrt{\pi }} $ cm. If the surface tension of water is 30 dynes per cm, then the work done will be[MP PMT 1986]

Options:

A) 180 ergs

B) 360 ergs

C) 720 ergs

D)960 ergs

Show Answer

Answer:

Correct Answer: C

Solution:

$ W=8\pi T(r _{2}^{2}-r _{1}^{2}) $

$ =8\pi T\left[ {{\left( \frac{2}{\sqrt{\pi }} \right)}^{2}}-{{\left( \frac{1}{\sqrt{\pi }} \right)}^{2}} \right] $ W = $ 8\times \pi \times 30\times \frac{3}{\pi } $

$ =720\ erg $



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