Question

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

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

Answer 1

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