Sol. The cross-sectional edge of the disc of water is a semicircle of radius r = d (see figure). Thus, the curvature of the surface of the water is 2/d, which corresponds to a pressure of curvature of p = 2 γ /d, where γ is the surface tension. (The other component of the curvature is negligible because D >> d.)

The pressure inside the disc is therefore p 0 – 2 γ /d when the atmospheric pressure is p 0 . This pressure difference acts over a surface area between the water and each of the glass surfaces of π D 2 /4. This implies that a force,

F =

‘pulls' the glass plates together.