Surface Tension

By MRS (JM)

Surface Tension

Open Ended

Do you know :

Why insects like mosquitoes can walk on the surface of water?

Water droplets are round in shape?

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Surface Tension is the phenomenon due to which the free surface of a liquid behaves like a stretched membrane.

Definition: Surface Tension is the force per unit length in the plane of the liquid surface, acting at right angles on either side of an imaginary line drawn in that surface.

SI unit: N/m, Dimensional formula: ​MT-2

Surface Tension

Open Ended

Can you cite some examples that you can relate with surface tension???

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​Cohesive and Adhesive Forces

Cohesion: Force between similar molecules

Adhesion: Force between dissimilar molecules ​

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Molecular theory of Surface Tension

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Liquid Meniscus in narrow glass tube

​Angle of Contact

Angle of contact id the angle between the tangent to the liquid surface and tangent to the solid surface inside the liquid

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​Work done in stretching liquid surface

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​F=T X 2l

W= F X dx

W=T X 2l X dx

W= T X dA

where dA is the increased area​

​Capillarity

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​The tendency of a liquid in a capillary tube or absorbent material to rise or fall as a result of surface tension.

Is there a difference between a water drop and a bubble?

What?​

​Think in terms of number of free surfaces

Multiple Choice

How many free surfaces does a soap bubble has

• one

• two

• four

• none

Multiple Choice

How many free surfaces does a water drop has?

• one

• two

• three

• four