In this article, we will be looking at the concepts and definitions of Surface Tension and Capillary Action, and related terms.
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- Surface tension occurs at the interface of the liquid and a gas or at the interface of two liquids.
- Surface tension (σ) is inversely proportional to temperature.
- It acts when fluid is at rest.
- It is a surface phenomenon.
- It is force per unit length (N/m).
- It is due to cohesion only.
- For the water-air interface at 20 °C, its value is 0.0736 N/m.
- At the critical point, liquid-vapor states are same therefore σ = 0.
Pressure inside a drop (Solid like a sphere)
P = 4σ/d
Pressure inside Bubble
P = 8σ/d
Pressure inside Jet
P = 2σ/d
Here d = diameter of a drop
P = Gauge Pressure
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- Capillary Action is due to cohesion and adhesion, both.
- For capillary action diameter of the tube should be less than 3 cm.
Height of Water in Capillary Tube
h = 4σcos θ/ρgd
Where, h = rise in capillary
σ = surface tension of water and glass
d = diameter of a tube
θ = Angle of contact between the liquid and material
- For water and glass take θ = 0 degree
- For mercury and glass take θ = 128 degree
When Liquid surface supports another Liquid of Density ‘ρb’ then Rise is given by
h = 4σcos θ/(ρ – ρb)gd
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