Figure shows a capillary tube of radius r dipped into water. If the atmosphere pressure is `P_0`, the pressure at point A is

Options

A. `P_(0)`
B. `P_(0)+(2s)/(r)`
C. `P_(0)-(2s)/(r)`
D. `P_(0)-(4s)/(r)`

Answer

C

Explanation

`P_(A)=P_(0)-(2S)/(r)`
The pressure inside a concave meniscus is less than the pressure outside (atmospheric). Assuming the meniscus to be spherical (as for thin capillaries), excess pressure is `(2S)/(r)` where r is the radius of the hemispherical surface.