If  FC and FA  denote cohesive and adhesive forces on a liquid molecule near the surface of  solid, Then the surface of liquid is concave, when

When the liquid surface remains horizontal, the resultant force FR→  on the molecule must be vertically downward as shown in fig-(1) and the FR→ must always remain perpendicular to the free surface of liquid. In this case  FA = FCsin450 = Fc2                                  If  FA> Fc2 , the resultant force FR→  on the molecule will be as shown in fig-(2). Since FR→  must always be perpendicular to the free surface of liquid, the free surface will be concave in this case.