PPT - Electrical Conductivity in Metals - Civil Engineering (CE) PDF Download

 Page 1


INTRODUCTION  
Lecture-1
?The electron theory of solids 
aims to explain the structures and 
properties of solids through their 
electronic structure.
?The electron theory of solids has 
been developed in three main 
stages.
www.calicutbtech.in
Page 2


INTRODUCTION  
Lecture-1
?The electron theory of solids 
aims to explain the structures and 
properties of solids through their 
electronic structure.
?The electron theory of solids has 
been developed in three main 
stages.
www.calicutbtech.in
(i). The classical free electron theory:
Drude and Lorentz developed this theory in 
1900. According to this theory, the metals 
containing free electrons obey the laws  of 
classical mechanics.
(ii). The Quantum free electron theory:
Sommerfeld developed this theory during 
1928. According to this theory, the free 
electrons obey quantum laws.
-
Page 3


INTRODUCTION  
Lecture-1
?The electron theory of solids 
aims to explain the structures and 
properties of solids through their 
electronic structure.
?The electron theory of solids has 
been developed in three main 
stages.
www.calicutbtech.in
(i). The classical free electron theory:
Drude and Lorentz developed this theory in 
1900. According to this theory, the metals 
containing free electrons obey the laws  of 
classical mechanics.
(ii). The Quantum free electron theory:
Sommerfeld developed this theory during 
1928. According to this theory, the free 
electrons obey quantum laws.
-
(iii). The Zone theory:
Bloch stated this theory in 1928.  
According to this theory, the free 
electrons move in a periodic field 
provided by the lattice.  This theory 
is also called “Band theory of solids”.
Page 4


INTRODUCTION  
Lecture-1
?The electron theory of solids 
aims to explain the structures and 
properties of solids through their 
electronic structure.
?The electron theory of solids has 
been developed in three main 
stages.
www.calicutbtech.in
(i). The classical free electron theory:
Drude and Lorentz developed this theory in 
1900. According to this theory, the metals 
containing free electrons obey the laws  of 
classical mechanics.
(ii). The Quantum free electron theory:
Sommerfeld developed this theory during 
1928. According to this theory, the free 
electrons obey quantum laws.
-
(iii). The Zone theory:
Bloch stated this theory in 1928.  
According to this theory, the free 
electrons move in a periodic field 
provided by the lattice.  This theory 
is also called “Band theory of solids”.
The classical Free Electron Theory of 
Metals (Drude - Lorentz theory of metals
postulates :
(a). In an atom electrons revolue around the nucleus and 
a metal is composed of such atoms.
(b). The valence electrons of atoms are free to move 
about the whole volume of the metals like the 
molecules of a perfect gas in a container. The 
collection of valence electrons
from all the atoms in a given piece of metal forms 
electrons gas. It is free to move throughout the 
volume of the metal
Lecture-2
www.calicutbtech.in
Page 5


INTRODUCTION  
Lecture-1
?The electron theory of solids 
aims to explain the structures and 
properties of solids through their 
electronic structure.
?The electron theory of solids has 
been developed in three main 
stages.
www.calicutbtech.in
(i). The classical free electron theory:
Drude and Lorentz developed this theory in 
1900. According to this theory, the metals 
containing free electrons obey the laws  of 
classical mechanics.
(ii). The Quantum free electron theory:
Sommerfeld developed this theory during 
1928. According to this theory, the free 
electrons obey quantum laws.
-
(iii). The Zone theory:
Bloch stated this theory in 1928.  
According to this theory, the free 
electrons move in a periodic field 
provided by the lattice.  This theory 
is also called “Band theory of solids”.
The classical Free Electron Theory of 
Metals (Drude - Lorentz theory of metals
postulates :
(a). In an atom electrons revolue around the nucleus and 
a metal is composed of such atoms.
(b). The valence electrons of atoms are free to move 
about the whole volume of the metals like the 
molecules of a perfect gas in a container. The 
collection of valence electrons
from all the atoms in a given piece of metal forms 
electrons gas. It is free to move throughout the 
volume of the metal
Lecture-2
www.calicutbtech.in
(c) These free electrons move in random directions and 
collide with either positive  ions fixed to the lattice or 
other free electrons. All the collisions are elastic i.e., 
there is no loss of energy. 
(d). The movements of free electrons obey the laws of 
the classical kinetic theory of gases.
(e). The electron velocities in a metal obey the classical 
Maxwell – Boltzmann distribution of velocities.