Explain the following:
(i) Drops of liquid assume a spherical shape.
(ii) The level of mercury in a capillary tube is lower than the level outside when a capillary tube is inserted in mercury.
(i) The spherical shape of drops: Surface tension accounts for the spherical shape of liquid drops. The effect of the surface tension is to decrease the surface area of the liquid to a minimum. Hence, liquid drops become spherical because a sphere has a minimum surface area for a given volume.
(ii) Fall of the mercury level in a capillary tube. This is because the force of attraction between the mercury molecules (cohesive forces) is greater than the adhesive forces between mercury and glass. This induces mercury to detach from the surface of the glass and level of the mercury goes down in the capillary tube.
