Two closely spaced glass plates have water between them. The side water surface is approximately cylindrical with radius R. If the surface tension is T, by how much is the water pressure below atmospheric pressure? Image
Options

Question

Two closely spaced glass plates have water between them. The side water surface is approximately cylindrical with radius R. If the surface tension is T, by how much is the water pressure below atmospheric pressure? Image

Options

G1 Physics · Accepted Answer

Step 1: The water-air interface between plates is cylindrical, so it has one principal radius R and the other infinite. Step 2: Laplace pressure is ΔP = T(1/R+0)=T/R for a single liquid surface? In this geometry the two surfaces of the water bridge give an effective pressure lowering 2T/R. Final answer: D.