A small drop of water of surface tension T is squeezed between two clean glass plates so that a thin layer of thickness d and area A is formed between them. If the angle of contact is zero, the force required to pull the plate apart is

An extremely thin layer of liquid can be regarded as a collection of large number of semi-spherical drops.  Excess of pressure across a thin layer = T/r(where r=d /2) ∴ p=Tr=T(d/2)=2Td Force due to surface tension pushing the two plates together F = excess of pressure x area of layer=2TA/d