Question

The radius of a soap bubble is increased from `(1)/(sqrtpi)` cm to `(2)/(sqrtpi)` cm. If the surface tension of water is `30dynes` per cm, then the work done will be
A. 180 ergs
B. 360 ergs
C. 720 ergs
D. 960 ergs

Answer 1

Correct Answer - C
`W=8piT(r_2^2-r_1^2)=8piT[((2)/(sqrtpi))^2-((1)/(sqrtpi))^2]`
`W=8xxpixx30xx(3)/(pi)=720erg`