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 plate. Let S be the surface tension of water `P_(0)=` atmospheric pressure, `P=` pressure of water just below the water surface in the region between the plates-
A. `p_(0) - (2S)/(r)`
B. `p_(0) + (2S)/(r)`
C. `p_(0) - (4S)/(r)`
D. `p_(0) + (4S)/(r)`

Answer 1

Correct Answer - A
Here, the free liquid surface between the plates will be cylindrical which is curved along one axis (parallel to the plates). The radius of curvature of meniscus, R = r/2. For cylindrical surface, `p_(0) - p = (S)/(R) = (S)/(r//2) = (2S)/(r) rArr p = p_(0) - (2S)/(r)`