किसी द्रव पृष्ठ के अवतल भाग की ओर का दाब उत्तल भाग की ओर के दाब से अधिक क्यों होता है ? समझाइए |

Explanation

If the free surface of a liquid is plane, then the surface tension acts horizontally. It has no component perpendicular to the horizontal surface. As a result, there is not pressure difference between the liquid side and the vapour.

If the surface of the liquid is concave, then the resultant force R due to surface tension on a molecule on the surface act vertically upwards. To balance this, an excess of pressure acting downward on the concave side is necessary. On the other hand if the surface is convex, the resultant R acts downwards and there must be an excess of pressure on the concave side acting in the upwards direction.
Thus, there is always an excess of pressure on the concave side of a curved liquid surface over the pressure on its convex side due to surface tension.