Question

A frame made of metalic wire enclosing a surface area A is covered with a soap film. If the area of the frame of metallic wire is reduced by `50%` the energy of the soap film will be changed by:
A. `100%`
B. `75%`
C. `50%`
D. `25%`

Answer 1

Correct Answer - C
Surface energy = surface tension `xx` surface area
`E=Txx2A`
New surface energy,
`E_(1)=Txx2((A)/(2))=TxxA`
% decrease in surface energy
`=(E-E_(1))/(E)xx100`
`=(2TA-TA)/(2TA)xx100=50%`