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 $
