# The Angle of Contact (Surface Tension) – concepts

In this post, we will discuss the concepts of the **Angle of Contact** which is related to surface tension. Let’s define and understand it first.

## Define the Angle of Contact

How much curved a meniscus will be, is expressed in terms of angle of contact. The angle of contact, θ; between a liquid and a solid is the angle enclosed between the tangents to the liquid surface and the solid surface measured inside the liquid. (see the figure below)

## Angle of Contact is an acute angle for a concave meniscus and it is an obtuse angle for a convex meniscus – explain

Figure 1 (a) shows a concave meniscus and Figure 1 (b) convex meniscus.

P is a point of contact of liquid with the glass wall. PQ is tangent at P to meniscus.

**Angle RPQ is the angle θ of contact.**

*Obviously, θ is the acute angle for a concave meniscus and is an obtuse angle for a convex meniscus.*

## Angle of Contact depends on these factors

**The value of Angle of Contact θ depends on**

(i) nature of liquid and solid in contact

(ii) the nature of the medium above the free surface of the liquid.

And, θ does not depend on the inclination of the solid to the liquid surface.

## Angle of Contact examples

The angle of contact of mercury with glass is about 1400.

The angle of contact for water and glass is about 8^{0}–10^{0}.