dielectrics
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Popat S. Tambade
Electric dipole• Two equal and opposite charges separated by a small distance form
an electric dipole
- +
d
- q + q
O Axial line
Equatorial line
The product of the magnitude of either charge and the distance between the charges is called electric dipole moment p = qd
Unit of dipole moment is coulomb – metre or C-m
p = qdIt is directed along the axis of dipole and from – q to + q
Electric dipole moment :
p
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-
+
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Effect of Electric Field
- +±-
+
Non polar molecule
Polar molecule E
E
Dipole moment is induced along the direction of field
Dipole moment is oriented along the field direction
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C OO+ +- -
C+ +
O-
O-
p = p1 + p2 = 0 p1 = - p2
p1 p2
p = p1 + p2 = 0 p1 = - p2
Resultant dipole moment is along the direction of electric field
p1 p2
Non polar
CO2 molecule
E
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O
HH
- -
+ +
EO
HH
- -
+ +
p1p2
p
p = p1 + p2 Polarp
H2O molecule
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- +±
- +±
- +±
- +±
- +±
- +±
- +±
- +±
- +±
- +±
- +±
- +±
- +±
- +±
- +±
- +±
- +±
- +±
- +±
- +±
- +±
- +±
- +±
- +±
- +±
- +±
- +±
- +±
- +±
- +±
- +±
- +±
+
+
+
+
+
+
+
+
-
-
-
-
-
-
-
-
E'
Polarization of non polar dielectric material
E0
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- +
- +
- +
- +
- +
- +- +
- +
- +
- +
- +
- +- +
- +
-
+
- +
- +
- +
- +
- +- +
- +
- +
- +
- +
- +
- +- +
- +
- +- +
- +
E'
Polarization of polar dielectric material
E0
+
+
+
+
+
+
+
+
-
-
-
-
-
-
-
-
E
E0E E'= -
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- - - -
-
- - - - -
- - - - -
-
- - - - -
-
- - - - -
-
- - - - -
Polarization of material
+ + + + +
+ + + + +
+ + + + + +
+ + + + + +
+ + + + +
+ + + + +
t
A
p
+q' Net Dipole moment is p = q' t Volume of slab = A t
Electric polarization vector P = pV
P = q' t A t
q' A
=
Thus, polarization is induced charge per unit area. It’s unit is C/m2
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- +
- +
- +
- +
- +
- +
- +
- +
Polarization of polar dielectric material
E
D
P