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

Options

A. 1
B. 0.75
C. 0.5
D. 0.25

Answer

D

Explanation

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)`
% decrease in surface energy
`= (E xx E_(1))/(E) xx 100 = (2TA - TA//2)/(2TA) xx 100 = 75%`