Question

The figure shows capillary tube of radius $r$ dipped into water. The atmospheric pressure is $P_0$ and the capillary rise of water is $h.s$ is the surface tension for water-glass.
The pressure inside water at the point $A$ (lowest point of the meniscus) is

• A. $P_0$
• B. $P_0+\frac{2s}{r}$
• C. $P_0-\frac{2s}{r}$
• D. $P_0-\frac{4s}{r}$

Answer 1

The correct option is C $P_0-\frac{2s}{r}$

Since the pressure above the meniscus is $P_0$.
Difference between pressures outside and inside of the meniscus is 2s/r
Since Meniscus is concave upwards, this means pressure inside meniscus is less as compared to outside
So Pressure below the meniscus of radius $r$ is $P_0-2s/r$
( assuming meniscus to be spherical)