Question

A frame made of metallic wire enclosing a surface area A is covered with a soap film. If the area of the frame of metallic wire is reduced by 25%, the energy of the soap film will be changed by
A. 1
B. 0.75
C. 0.5
D. 0.25

Answer 1

Correct Answer - D
Surface energy = surface tension `xx` surface area
`E = T xx 2A`
New surface energy
`E_(1) = T xx 2(A//4)`
` =T xx A//2`
% decreaase in surface energy
`= (E-E_(1))/(E ) xx 100`
` = (TA - TA//2)/(2TA) xx 100 = 25%`