Saved Bookmarks
| 1. |
It is well known that water forms a concave meniscus while mercury forms a convex meniscus when they are present in a glass tube. This is because the (1) Density of mercury is more than that of glass while water has a density less than that of glass.(2) Force of cohesion, between water molecules is more than the force of adhesion between water and glass; the reverse in true for mercury.(3) Force of cohesion, between water molecules, is less that n the force of adhesion between water and glass; the reverse is true for mercury. (4) Excess of pressure, inside a water drop of radius r, is more than the corresponding excess of pressure inside a mercury drop of the same radius. |
|
Answer» Correct option: (3) Force of cohesion, between water molecules, is less that n the force of adhesion between water and glass; the reverse is true for mercury. Explanation: The shape of the meniscus, of a given liquid, in a given container, is determined primarily by the comparative magnitudes of the relevant forces of cohesion and adhesion. For liquids (like water), the force of cohesion between liquid molecules, is less than the force of adhesion between the liquid molecules and the molecules of the walls of the container (glass). In such a case, the liquid forms a concave meniscus. The reverse is true for mercury put in a glass tube. In such a case the liquid forms a convex meniscus. [Note: Option (4) is incorrect; the excess pressure (= 2T/r) is more for the mercury drop which has a higher value of surface tension]. |
|