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Angle of Contact

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Topics

Estimated time: 3 minutes
  • Angle of contact
  • Characteristics of angle of contact
  • Factors affecting angle of contact (θ)
    i) Nature of solid and liquid in contact
    ii) Impurities
    iii) Inclination
    iv) Temperature
  • Shape of liquid meniscus
  • Shape of liquid drop
Maharashtra State Board: Class 11

Definition: Angle of Contact

The angle between the surface of the solid and the tangent drawn to the surface of the liquid at the point of contact on the side of liquid is called the angle of contact of that liquid with that solid.

OR

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, is called the angle of contact.

Maharashtra State Board: Class 11

Formula: Angle of Contact Conditions

Case 1: θ < 90° (Concave Meniscus)

Fa > \[\frac {F_c}{\sqrt 2}\]
 
Adhesive force > Cohesive force → Liquid wets solid → Level rises in capillary

Case 2: θ = 90° (Plane/Horizontal Meniscus)

Fa = \[\frac {F_c}{\sqrt 2}\]
Adhesive force = Cohesive force → Liquid does not wet solid → Level remains unchanged
 
Case 3: θ > 90° (Convex Meniscus)
Fa < \[\frac {F_c}{\sqrt 2}\]
Adhesive force < Cohesive force → Liquid does not wet solid → Level falls in capillary
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