Two glass plates are separated by water. If surface tension of water is 75 dynes per cm and area of each plate wetted by water is 8 cm2 and the distance between the plates is 0.12 mm, then the force applied to separate the two plates is

The shape of water layer between the two plates is shown in the figure.Thickness d of the film = 0.12 mm = 0.012 cm. Radius R of cylindrical face =d2. F=T(2I)=P(I×2R)P=TRPressure difference across the cylindrical surface =TR=2Td.Area of each plate wetted by water = A.Force F required to separate the two plates is given byF= pressure difference × are a=2TdA =2×75×80.012=105dynes