# MHT-CET Physics Crash Course “Relation Between Surface Tension and Surface Energy” Class 12

## “Relation Between Surface Tension and Surface Energy” MHT-CET Class 12 Physics Crash Course | Chapter Mechanical Properties of Fluids

In this session G.S. Khairnar discussed the theory and MCQ’s of “Relation Between Surface Tension and Surface Energy”. The session will be useful for all the aspirants of MHT-CET 2022. The session will be in Marathi and English.

### Relation Between Surface Tension and Surface Energy:-

We know that to have minimum potential energy, molecules at liquid surface tend to reduces area to minimum value. Thus, liquid surface behave as a stretched membrane. This tendency of liquid surface is known as surface tension.

#### Surface Tension

It is defined as the force per unit length.

The force acting per unit length of imaginary line drawn on free liquid surface at right angles on either sides of the line.

If L is the length of line & F is the force acting on it, the surface tension (T) is given by,

Unit of surface tension in SI system is newton per meter (N/m)

In this article we are going to discuss the relation between surface tension and surface energy.

Let’s discuss the concept in details……………!

#### Surface energy

The potential energy per unit area of the liquid surface is called the surface energy.

Relation between surface energy & surface tension:

Consider, ABCD as open rectangular frame of wire on which a wire PQ can slide without friction. Dip the frame into soap solution, take out and hold horizontally so that the soap film AB’C’D if formed.

Due to the surface tension, a force of F acts on the wire LM of length ‘L’ tending to pull it towards AB given as,

∴ F = 2TL

[2-indicates that the soap solution has 2 surface, both of which are in contact with the wire.]

Imagine that the wire is pulled by infinitesimal small distance ‘dx’, then the work done during against the force of surface tension is given as,

∴ W = Force x displacement

∴ W = F dx

∴ W = 2TL dx

Now, the change in the surface area of the film is.

∴ A = 2Ldx

Hence, the mechanical work done per unit surface area is.

This work is stored in the form of potential energy by the surface. This poetical energy of thee surface per unit area is surface energy.

∴U = T.dA

∴ Surface energy per unit area = surface tension

Point to remember….!

### Let’s solve following MCQ’s…..

Q.1) Relation between surface tension and surface energy can be written as…..

a) Surface energy per unit area = surface tension

b) Surface tension per unit area = surface energy

c) Surface energy × surface tension = surface area

c) Surface energy × surface area = surface tension

a) Surface energy per unit area = surface tension

Q.2) Change in surface energy during blowing a bubble of liquid of surface tension T from radius r1 to r2 is …..

Q.3) SI unit of surface tension in terms of surface energy is …..

a) J/m

b) J/m2

c) m/J

c) m2/ J

b) J/m2

Q.4) Soap bubble of radius 5 cm is blown, amount work required for this if surface tension of soap solution is 64 dyne/cm is….

a) 004 joule

b) 04 joule

c) 4 joule

c) 4 joule

a) 004 joule

Q.5) Area of soap film formed on rectangular frame increased from 25 cm2 to 28 cm2. Amount of work done during the process if surface tension of soap film is 0.060 N/m is…

### ♦जिल्हा नुसार जाहिराती ♦

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रायगढ़ रत्नागिरि सांगली सातारा सिंधुदुर्ग सोलापुर
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### ♦शिक्षणानुसार जाहिराती ♦

७ वी (7th) दहावी (SSC) बारावी (HSC) डिप्लोमा आय.टी.आय पदवी
पदव्युत्तर शिक्षण बी.एड एम.एड एल.एल.बी / एल.एल.एम बीएससी एमबीए
बीसीए एमसीए बी.कॉम एम.कॉम GNM/ANM एमएससी
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बी.टेक एम.टेक MS-CIT