How does surface tension causes Capillary action?? pls explain

Question

masumanwar · Answer

The adhesive and cohesive force in the fluid make the action of capillary as a result of surface tension .

anonymous · Answer

pls explain 'adhesive and cohesive force' section...

anonymous · Answer

It can be shown that for a drop or bubble  which is spherical the pressure inside  is equal to the pressure outside  plus twice the surface tension divided by the radius of the drop/bubble.  In other words the surface tension is balancing the internal and external pressures. If it didn't the bubble would burst or collapse.

When a narrow tube is put into a liquid   the liquid wets the surface of the walls of the tube  the surface of the liquid is spherical  for small diameter tubes. This is half a bubble and the atmospheric  pressure above the liquid is forcing the surface downward indicating that the atmospheric pressure is higher than the internal pressure of the liquid at the surface. But the liquid is in equilibrium and not moving so the forces at the surface must balance. This unequal pressures must be compensated by another pressure  in this case due to the height of the liquid column.  See the diagram.