•    When a small diameter tube less than 6mm is inserted vertically inside a pool of liquid, the liquid level in the tube either rise or falls relatively to the liquid level in the pool.

•    This phenomenon of rise or fall of liquid level in the capillary tube is called as capillarity. Capillarity is due to cohesion and adhesion.

•    If the adhesion force between molecules of liquid and tube is more than cohesion between
liquid molecules (e.g. water), the liquid will wet the glass surface and the liquid level will rise.

•    The liquid level will become concave upward as shown in.

Capillary rise

•    In such case angle between surface tension with the vertical (θ) is less than 90⁰

•    If cohesive force between molecules of liquid and tube is more than cohesion between liquid molecules (If cohesive force predominate)

•    e.g. mercury, the liquid does not wet the surface, liquid level will fall as shown in.



•    The liquid become convex upwards in such case angle between surface tension with the vertical (θ) is greater than 90⁰

•    e.g. suction of kerosene in lamp, rise of water in soil are examples of capillarity.

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