The angle which the tangent make to the free surface of the liquid at the point of contact with the walls of the vessel inside the liquid is called the angle of contact, or it is defined as the angle subtended between the tangents drawn at the liquid surface and the solid surface inside the liquid at the point of contact is called the angle of contact (θ).
- The angle of contact depends upon the liquid’s nature and the solid in contact and the medium which exists above the free surface of the liquid.
- The angle of contact increases with an increase in the temperature of the liquid.
- The angle of contact decreases on adding soluble impurity to a liquid.
Importance of angle of contact
The contact angle determines whether a liquid will spread on the surface of a solid or form droplets on it.
- If the Angle of contact is obtuse: then a droplet will be formed.
- If the Angle of contact is acute: then the water will spread.