A thin soap film is formed in a recangular frame of area ` 15 xx 10^(-4) m^(2)` . The energy required to increase its area to `35 xx 10^(-4) m^(2)` is

Options

A. ` 6 xx 10^(-5)`J
B. `12 xx 10^(-5)`J
C. `20 xx 10^(-4)`J
D. `25 xx 10^(-4)`J

Answer

B

Explanation

W = 2 change in surface area `xx` surface tension
` = T xx 2(A_(2)-A_(1))`
` = 2 xx 20 xx10^(-4)m^(-2)xx3xx10^(-2)` N/m
` = 12 xx 10^(-5)` J