UNIT-1-Conducting Materials
1. Define electrical conductivity.
The electrical conductivity is defined as the quantity of electricity flowing
per unit time maintained at unit potential gradient.
2. Define mobility of electrons.
When electric field is applied to metals, the electrons moves in the
direction opposite to the field direction with the velocity ‘v’ then the
mobility of an electron is defined as the velocity acquired by the electron
per unit electric field.
3. Give the postulates of classical free electron theory.
✔According to this theory, a metal consists of electrons which are
free to move about in the crystal molecules of a gas it contains
mutual repulsion between electrons is ignored and hence potential
energy is taken as zero. Therefore, the total energy of the electron
is equal to its kinetic energy.
✔In the absence of electric field (E=0), the free electrons in meta
move in random directions and collide with each other.
✔During this collision no loss of energy is observes since the
collisions are elastic.
✔When electric field is applied, the free electrons are accelerated in
the direction opposite to the direction of applied electric field
4. Distinguish between relaxation time and collision time.
Relaxation time Collision time
It is the time taken by the It is the average time taken
free electron to reach its by a free electron between
equilibrium position from its two successive collisions.
disturbed position, due to
field applied.
𝜏 = 10−14s
5. Define drift velocity and give its formula.
Drift velocity is defined as the average velocity acquired by the free
electron in a particular direction, due to application of field.
, 6. Define mean free path
The average distance travelled between two successive collisions is
called mean free path. It is denoted by letter 𝜆.
7. Mention any two important features of quantum free electron
theory of metals.
It shows that the energy levels of an electron are discrete.
The maximum energy level upto which electrons can be filled is
denoted by Fermi energy level.
8. Define Weidemann franz law
Weidemann franz law is defined as the ratio between the thermal
conductivityand electrical conductivity of a metal is directly
proportional to absolute temperature of the metal.
9. What are the differences between drift velocity and thermal
velocity?
Drift velocity Thermal velocity
Drift velocity is the average Thermal velocity is the velocity
velocity acquired by the free of an electron without any
electron, in the presence of external field.
electric field.
1. Define electrical conductivity.
The electrical conductivity is defined as the quantity of electricity flowing
per unit time maintained at unit potential gradient.
2. Define mobility of electrons.
When electric field is applied to metals, the electrons moves in the
direction opposite to the field direction with the velocity ‘v’ then the
mobility of an electron is defined as the velocity acquired by the electron
per unit electric field.
3. Give the postulates of classical free electron theory.
✔According to this theory, a metal consists of electrons which are
free to move about in the crystal molecules of a gas it contains
mutual repulsion between electrons is ignored and hence potential
energy is taken as zero. Therefore, the total energy of the electron
is equal to its kinetic energy.
✔In the absence of electric field (E=0), the free electrons in meta
move in random directions and collide with each other.
✔During this collision no loss of energy is observes since the
collisions are elastic.
✔When electric field is applied, the free electrons are accelerated in
the direction opposite to the direction of applied electric field
4. Distinguish between relaxation time and collision time.
Relaxation time Collision time
It is the time taken by the It is the average time taken
free electron to reach its by a free electron between
equilibrium position from its two successive collisions.
disturbed position, due to
field applied.
𝜏 = 10−14s
5. Define drift velocity and give its formula.
Drift velocity is defined as the average velocity acquired by the free
electron in a particular direction, due to application of field.
, 6. Define mean free path
The average distance travelled between two successive collisions is
called mean free path. It is denoted by letter 𝜆.
7. Mention any two important features of quantum free electron
theory of metals.
It shows that the energy levels of an electron are discrete.
The maximum energy level upto which electrons can be filled is
denoted by Fermi energy level.
8. Define Weidemann franz law
Weidemann franz law is defined as the ratio between the thermal
conductivityand electrical conductivity of a metal is directly
proportional to absolute temperature of the metal.
9. What are the differences between drift velocity and thermal
velocity?
Drift velocity Thermal velocity
Drift velocity is the average Thermal velocity is the velocity
velocity acquired by the free of an electron without any
electron, in the presence of external field.
electric field.
