Dielectric materials can be polarized by an external electric field due to various polarization mechanisms. The dielectric constant is a measure of how much a material polarizes in response to an applied electric field. It is defined as the ratio of the relative permittivity of the medium to the permittivity of free space. The main polarization mechanisms are electronic, ionic, orientational, and space charge polarization. Electronic polarization occurs due to displacement of electrons relative to atomic nuclei. Ionic polarization is due to displacement of positive and negative ions relative to each other within molecules.

2. Dielectric Constant and
Polarizibality
Presented by: JUNAID HASSAN

3. Introduction:
Dielectric are the materials having electric dipole moment permanently.
• Dipole: A dipole is an entity in which equal positive and negative charges are
separated by a small distance.
• Dipole moment (μ 𝒆𝒍𝒆
): The product of
magnitude of either of the charges and
separation distance b/w them is Dipole moment.
μ 𝑒
= q.x

4. • Permittivity of free space:
The permittivity of free space, ε0, is a physical constant used often in
electromagnetism. It represents the capability of a vacuum to permit electric fields.
𝜀°=8.85418782 × 10-12 m-3 kg-1 s4 A2
• Permittivity of medium:
It is the measure of resistance of a medium in an electric field, it is denoted by Greek
letter epsilon (ε).
• Dielectric Constant:
the ratio between the permittivity of medium to the permittivity of free space.
𝜀 𝑟 =
𝜀
𝜀°

5. • The characteristics of a dielectric medium are determined by the dielectric
constant and it has no units.
• Polarizability :
Polarizability is the ability to form
instantaneous dipoles. It is a property of
matter. Polarizabilities determine the
dynamical response of a bound system
to external fields, and provide insight into
a molecule's internal structure.

6. Dielectric constant
• Dielectric constant is a measure of the degree to which a medium can resist
the flow of charge. It is defined as the ratio for the electric displacement D
to the electric field intensity E, i.e.
----------(1)
• Where is the relative permittivity of the medium and is the
permittivity of the free space.

7. • In the absence of a dielectric inside the capacitor, the field produced by the charges is
,which can be determined by measuring the potential difference across the
capacitor using the relation
0E 0V
0
0
(2)
L
V
E  

8. • Where L is the distance between the plates. When a dielectric slab is
introduced between the plates, the field polarize the medium. Which in
turn modifies the field to a new value E. this field can be determined by
measuring the new potential difference V across the capacitor using the
relation
----------(3)
0E
V
E
L


9. The dielectric constant in terms of the field and E is given by the relation
-------------(4)
From equation 2 and 3, then
-------------(5)
Similarly dielectric constant by measuring capacitor of condenser with and without
dielectric and taking the ratio as
------------(6)
As the ratio for the charge Q on either plate to the potential difference b/w the plate as
0E
0
r
E
E
0
r
V
V
0
C
r
c

Q
C
V


10. From eq. 4
The polarization produced in the material is a measure of the charge in the capacitance
such that
where is the electric susceptibility.
In a non cubic crystal the dielectric response is described by the components of the
susceptibility tensor or dielectric constant tensor.
0
r
E E

0
0
0
0
( )
( )
( 1)
1 1
r
r e
P c V
E
E
P
E
C

 
  
 
   

 


0
e
P
E
 


11. Polarization
• What is Polarization?
• Polarization, in Physics, is defined as a phenomenon caused due to the wave nature
of electromagnetic radiation. Sunlight travels through the vacuum to reach the
Earth, which is an example of an electromagnetic wave. These waves are called
electromagnetic waves because they form when an electric field interacts with a
magnetic field. In the chapter on waves, you learned about two types of waves,
transverse waves, and longitudinal waves.

12. One type of transverse wave
• Transverse waves
• Transverse waves are waves, i.e. movement of the particles in the wave is
perpendicular to the direction of motion of the wave. For example, the
ripples when you throw a stone in water. Longitudinal waves are when the
particles of the medium travel in the direction of motion of the waves. For
example, the motion of sound waves through the air.

13. Types
Types of Polarization
Following are the three types of polarization depending on the transverse and longitudinal
wave motion:
•Linear polarization
•Circular polarization
•Elliptical polarization
Linear polarization
In linear polarization, the electric field of light is limited to a single plane along the direction of
propagation.
Circular Polarization
There are two linear components in the electric field of light that are perpendicular to each
other such that their amplitudes are equal, but the phase difference is π2. The propagation of
occurring electric field will be in a circular motion.
Elliptical Polarization
The electric field of light follows an elliptical propagation. The amplitude and phase difference
between the two linear components are not equal.

14. • Polarization Applications
• Following are the applications of polarization:
• Polarization is used in sunglasses to reduce the glare.
• Polaroid filters are used in plastic industries for performing stress analysis test.
• Three-dimensional movies are produced and shown with the help of polarization.
• Polarization is used for differentiating between transverse and longitudinal waves.
• Infrared spectroscopy uses polarization.
• In Chemistry, the chirality of organic compounds are tested using polarization technique.
• Stay tuned with BYJU’S to learn more about the polarization of light using the methods
listed above

15. ELECTRIC POLARIZATION
• The process of producing electric dipoles by an electric field is called electric
polarization in dielectrics.
POLARIZABILITY:
• The induced dipole moment per unit electric field is called polarizability.
• The induced dipole moment is proportional to the intensity of the electric field.
µ∝E
µ=E
 polarizability constant

16. VARIOUS POLARIZATION
PROCESSES
When the specimen is placed inside a D .c electric field polarization is due to
two types of processes.
1.Electronic polarization
2.Ionic polarization
3.Orientational polarization
4.Space charge polarization

17. ELECTRONIC POLARIZATION
When an electric field is applied to an atom positively charged nucleus
displaces in the direction of field and electron could in opposite direction .This kind
of displacement will produce an electric dipole within the atom.
i.e. dipole moment is proportional to the magnitude of field strength and is given by
µₑ∝E
µₑ=ₑE
Where ‘ₑ’ is polarizability constant.

18. IONIC POLARIZATION
• The ion polarization occurs when atoms forms molecules and it is mainly due to a
relative displacement of the atomic components of the molecule in the presence of
an electric field.
• When an electric field is applied to the molecule, the positive ions displaced by ꓫ₁ to
the negative side electric field and negative ions displaced by ꓫ₂ to the positive
side of the field.
• The resultant dipole moment µ=q(ꓫ₁+ꓫ₂)