Consider for simplicity a wire frame suspending a liquid film. If one bar of the frame is movable it is found that a force 5N per unit length must be applied to maintain the bar in position. If this force moves a small distance so that the total area of the film is increased by 0.5m2. Interfacial free energy per unit area is given as 4 J/m2. Calculate the change in interfacial energy? (Take the area of interface as 2m2)

Consider for simplicity a wire frame suspending a liquid film. If one

1.	Consider for simplicity a wire frame suspending a liquid film. If one bar of the frame is movable it is found that a force 5N per unit length must be applied to maintain the bar in position. If this force moves a small distance so that the total area of the film is increased by 0.5m2. Interfacial free energy per unit area is given as 4 J/m2. Calculate the change in interfacial energy? (Take the area of interface as 2m2)
A.	0.25 J
B.	0.50 J
C.	8J
D.	0.90 J
Answer» D. 0.90 J