Tiêu đề 1.5 Capillarity, Vapour pressure.pdf ✅

Capillarity • is defined as a phenomenon of rise or fall of a liquid surface in a small tube relative to the adjacent general level of liquid when the tube is held vertically in the liquid. • The rise of liquid surface is known as capillary rise while the fall of the liquid surface is known as capillary depression. • It is expressed in terms of cm or mm of liquid. • Its value depends upon the specific weight of the liquid, diameter of the tube and surface tension of the liquid
Expression for Capillary Rise • Consider a glass tube of small diameter 'd' opened at both ends and is inserted in a liquid, say water. The liquid will rise in the tube above the level of the liquid. • h= height of the liquid in the tube. • Under a state of equilibrium, the weight of liquid of height h is balanced by the force at the surface of the liquid in the tube. But the force at the surface of the liquid in the tube is due to surface tension σ = Surface tension of liquid θ= Angle of contact between liquid and glass tube. The weight of liquid of height h in the tube = (Area of tube x h) x ρ x g = π 4 d 2 x h x ρ x g ρ = density of liquid Vertical component of the surface tensile force = (σ x circumference) x cos θ = σ x πd x cos θ