Question

A soap bubble of radius `1//sqrtpi "cm"` is expanded to radius `2//sqrtpi "cm".` Calculate the work done. Surface tension of soap solution `=30 "dyne"" "cm^(-1).`
A. 120 erg
B. 360 erg
C. 720 erg
D. 240 ergs

Answer 1

Correct Answer - C
Work done ` = T xx 2 xx dA`
` = T [ 4pi (2/(sqrt(pi)))^(2) - 4pi (1/(sqrt(pi)))^(2)]2`
` = 30 xx 12 xx 2 = 720 ` erg