Question

Two very wide parallel glass plates are held vertically at a small separation d, and dipped in water. Some water climbs up in the gap between the plates. Let S be the surface tension of water, p₀ = atmospheric pressure, p = pressure of water just below the water surface in the region between the plates.

(a) p = p₀ - 2S/d

(b) P = p₀ + 2S/d

(c) p = p₀ - 4S/d

(d) p = p₀ + 4S/d

Answer 1

Correct Answer is: (a) p = p₀ - 2S/d

The free liquid surface between the plates is cylindrical, and hence is curved along one axis only (parallel to the plates). The radius of curvature r = d/ 2. p₀ - p = S/r.