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Angle of Contact

The angle of contact between a liquid and a solid is defined as the angle enclosed between the tangents to the liquid surface and the solid surface inside the liquid, both the tangents being drawn at the point of contact of the liquid with the solid (Fig. 18).

Fig. 18


Important Points
  • The value of angle of contact lies between 0° and 180°. θ = 0° for pure water and glass, θ = 8° for tap water and glass, θ = 90° for water and silver, θ = 138° for mercury and glass, θ = 160° for water and chromium.
  • It is particular for a given pair of liquid and solid. Thus, the angle of contact changes with the pair of solid and liquid.
  • It does not depend upon the inclination of the solid in the liquid.
  • On increasing the temperature, the angle of contact decreases.
  • Soluble impurities increase the angle of contact.
  • Partially soluble impurities decrease the angle of contact.

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