Name: Angle of Contact
Uploaded: 2019-07-19
Duration: 6 min 57 s
Description: What is the contact angle? Which factor does the contact angle depend on? Why does the contact angle for the same liquid on different surfaces differ? Let's...

Question

Surface tension exists in liquids; give its proof by taking two examples.

Accepted Answer

The free surface of a liquid is always in a state of tension and has a tendency to occupy the minimum possible area. This property of the liquid is called surface tension. We can demonstrate this nature of the liquid by the following
Experiments.

$1$ -Needle supported on the water surface. Take a greased needle of steel on a piece of blotting paper and place it gently over the water surface. The blotting paper soaks water and soon sinks down what the needle keeps floating. The floating needle causes a little depression. The forces $F, F$ due to surface tension of the curved surface are inclined as shown in the figure. The vertical components of these two forces support the weight of the needle.

$2$ - Endless weight thread on a soap film. If we take a circular frame of a stiff wire and dip it into a soap solution, A thin soap film is formed on the frame. If a wet endless thread loop is gently placed over the film, it takes any irregular shape. But when the film is pricked at the centre, The loop is stretched outwards and takes a symmetrical circular shape. This is because for a given length a circle has the maximum surface area and so the outer liquid film tries to occupy the minimum possible area like a stretched elastic membrane.

$1 .$ The free surface of a liquid is always in a state of tension.

$2 .$ Sphere occupies the least possible surface area.

$3 .$ Surface tension is the property of liquids, not of solids or gases.

Surface tension exists in liquids; give its proof by taking two examples.

Important Questions on Surface Tension

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