Define surface tension. State its S.I unit and
dimensions. State any two characteristics of
angle of contact. State any two applications of
capillarity
Answers
Answer:
Surface tension is the tendency of fluid surfaces to shrink into the minimum surface area possible. Have you noticed when you fill a glass up to the brim with water, you can still add a few more drops till it spills out? Or have you ever broken a thermometer and observed how the fallen mercury behaves? All these happen due to the surface tension of the surface. Let us understand the concept, surface tension definition along with its SI unit, formula and examples.
What is Surface Tension?
According to the definition of surface tension, it is the phenomenon that occurs when the surface of a liquid is in contact with another phase (it can be a liquid as well). Liquids tend to acquire the least surface area possible. The surface of the liquid behaves like an elastic sheet.
Surface tension is the tension of the surface film of a liquid caused by the attraction of the particles in the surface layer by the bulk of the liquid, which tends to minimise surface area.
Given below in a table is the surface tension of various liquids:
Liquid
Surface Tension (N/m)
Hydrogen
2.4
Helium
0.16
Water
72.7
Ethanol
22.0
Sodium Chloride
114
Surface tension definition lets us know that the surface tension mainly depends upon the forces of attraction between the particles within the given liquid and also upon the gas, solid, or liquid in contact with it.
If there is a small leaf or a paper clip placed on the surface of a glass of water, what causes it to float over it? Watch the video below to find out the answer.
52,115
What Causes Surface Tension?
Intermolecular forces such as Van der Waals force, draw the liquid particles together. Along the surface, the particles are pulled toward the rest of the liquid. Surface tension is defined as,
The ratio of the surface force F to the length L along which the force acts.
Mathematically, surface tension can be expressed as follows:
T=F/L
Where,
F is the force per unit length
L is the length in which force act
T is the surface tension of the liquid
What is the Unit of Surface Tension?
The SI unit of Surface Tension is Newton per Meter or N/m. Check other units in the table provided below.
SI Unit
N/m
CGS Unit
dyn/cm
Dimension of Surface Tension
As we know, surface tension is given by the formula,
Surface tension = F/L
We know that F = ma, substituting the value in the equation, we get
=ma/L
Equating the fundamental quantities into the equation, we get
=MLT-2L-1
Solving further, we get
=MT-2
Hence, the dimensional formula of surface tension is MT-2.
You may also want to check out these topics given below!
Relation Between Viscosity And Density
Darcy Weisbach Equation
Hydrostatic Paradox
Fluid Dynamics
Examples of Surface Tension
Water striders, which are small insects, can walk on water as their weight is considerably less to penetrate the water surface. Like this, there are various examples of surface tension which are found in nature. Some cases are provided below:
Insects walking on water
Floating a needle on the surface of the water.
Rainproof tent materials where the surface tension of water will bridge the pores in the tent material
Clinical test for jaundice
Surface tension disinfectants (disinfectants are solutions of low surface tension).
Cleaning of clothes by soaps and detergents which lowers the surface tension of the water
Washing with cold water
Round bubbles where the surface tension of water provides the wall tension for the formation of water bubbles.
This phenomenon is also responsible for the shape of liquid droplets.
How to Calculate Surface Tension?
Here is an example of calculating surface tension by using the formula.
Compute the surface tension of a given liquid whose dragging force is 7 N and length in which the force acts is 2 m?
Solution:
Given,
F = 7 N
L = 2 m
According to the formula,
T = F/L
⇒ T = 7/2
⇒ T = 3.5 N/m
Methods of Measurement
Some methods of measurement of surface tension are given in the points below:
Spinning drop method
Pendant drop method
Du Noüy–Padday method
Du Noüy ring method
Wilhelmy plate method
Pendant drop method
Stalagmometric method
Capillary rise method
Bubble pressure method
Resonant oscillations of a spherical and hemispherical liquid drop
The vibrational frequency of levitated drops
Sessile drop method
Frequently Asked Questions – FAQs
Why is raindrop spherical?
Because of surface tension.
What happens when a soap bubble is charged?
It expands.
What is the dimensional formula of surface tension?
The dimensional formula of surface tension is: [ML0T-2].
What is the surface tension of water at its boiling point?
The surface tension of water at its boiling point..
Explanation:
Hope it helps u..