COMEDK Exam 2020 Solved Paper

(c) Given, initial surface area, A1=A
Final surface area, A2=A1−50% of A
A2=A−50%ofA=A−

A

2

=

A

2

Initial surface energy, E1=T‌cdot‌2‌A=2TA
Final surface energy, E2= Surface tension × Surface area
⇒E2&=T×2(A1−A2)
=T×2(A−

A

2

)
=T×2×

A

2

⇒E2=TA
∴ Percentage change in the energy of soap film=

E1−E2

E1

×100
=

2TA−TA

2TA

×100
=50%