Question

What Causes Capillary Pressure?

Answer 1

1. The pressure difference across the interface separating two insoluble fluids is known as capillary pressure.
2. The interfacial tension that exists at the contact separating two immiscible fluids causes capillary pressure.
3. The imbalance in the molecular forces of attraction experienced by the molecules at the surface causes interfacial tension.
4. There are enough molecules to balance out the net force experienced by molecules in the interior, the net force experienced is zero.
5. Capillary action is the resultant of intermolecular attraction between the molecules of the liquid and the adhesive force between the walls of the capillary and the liquid. This can be divided to three different situations as given below.
6. 
   1. The intermolecular attraction and the adhesive force cancel each other resulting in a zero capillary pressure.
   2. The intermolecular attraction $<$ the adhesive force resulting in a capillary pressure which causes the liquid level in the capillary column to rise.
   3. The intermolecular attraction $>$ the adhesive force resulting in a capillary pressure which causes the liquid level in the capillary column to descend.