Engineering physics 1(Electrical conductivity)

1 ENGINEERING PHYSICS
Mr. Gouri Kumar Sahu
Sr. Lecturer in Physics.
ENGINERING PHYSICSENGINERING PHYSICSENGINERING PHYSICSENGINERING PHYSICSENGINERING PHYSICSENGINERING PHYSICSENGINERING PHYSICSENGINERING PHYSICS
Senior Lecturer in Physics
C.U. T. M.

SESSION-2
2.1. Electrical Conduction
Electrical conductivity of a material is defined in terms of ease
with which a material transmits an electrical current. Electrical
current (I) is flow of electrons, and driving force for the flow of
electrons is called voltage (V). Ohm’s law relates these
parameters as follows
V α I
V = IR……………………………….……….[1.1]
where R – is the materials resistance to flow of electrons through
it.
V, I, and R respectively have units as volts, amperes, and ohms (Ω).

SESSION-2
2.2.Electrical Resistivity
Electrical resistance of a material is influenced by its
geometric configuration; hence a new parameter
called electrical resistivity (ρ) is defined such as it is
independent of the geometry.
ߩ ൌ
ோ஺
௟
……………………………..……….[1.2]
where A = cross-sectional area perpendicular to the
direction of the current
l – the distance between points between which the voltage
is applied.
Units for ρ are ohm-meters (Ω-m).

SESSION-2
2.3.Electrical Conductivity
Reciprocal of the electrical resistivity, known as electrical
conductivity (σ), is used to express the electrical behavior of a
material, which is indicative of the ease with which a material
allows of flow of electrons.
ߪ ൌ
ଵ
ఘ
ൌ
௟
ோ஺
…………………………..……..[1.3]
units: (Ω-m)-1 or mho/meter.
It depends on the presence of free electrons or conduction electrons, which
move freely in the metal and do not correspond to any atom.
These electrons are known as electron gas.

SESSION-2
2.4. Classification of Conducting Materials
materials can be classified into three categories:
I. Zero resistivity materials
II. Low resistivity materials
III. High resistivity materials
1. Zero resistivity materials:
1. Superconductor like alloys of aluminium, zinc, gallium,
nichrome, niobium, etc.
2. zero resistance below the transition temperature.
3. Perfect diamagnetic.
4. Used for energy saving in power systems, superconducting
magnets, memory storage elements.

SESSION-2
2.4. Classification of Conducting Materials
II. Low resistivity materials:
1. Metals and alloys like silver, aluminium etc.
2. Very high electrical conductivity, in the order of
10଼ Ωିଵ݉ିଵ.
3. Used as resistors. Conductors, electrical contacts,
etc. in electrical devices.
III. High resistivity materials:
1. Material like tungsten, platinum, nichrome, etc.
2. High resistivity and low temperature coefficient of
resistances.
3. Used in the manufacturing of resistors, heating
elements, resistance thermometers, etc.

SESSION-2
2.5.Basic Terminologies
Bound Electrons:
All the valence electrons in an isolated atom are bound to their
parent nuclei are called as bound electrons.
Free electrons:
Electrons which moves freely or randomly in all directions in the
absence of external field.
Drift Velocity
The average velocity of an electron in a conductor under the
influence of external electric field.

SESSION-2
2.5.Basic Terminologies
Electric Field (E):
The electric field E of a conductor having uniform cross section is defined as the
potential drop (V) per unit length (l).
i.e., E = V/ l V/m
Current density (J):
It is defined as the current per unit area of cross section of an imaginary plane
hold normal to the direction of the flow of current in a current carrying
conductor.
J = I/ A Am-2
Fermi level
Fermi level is the highest filled energy level at 0 K.
Fermi energy
Energy corresponding to Fermi level is known as Fermi energy.

END OF SESSION -2
THANK YOU

Engineering physics 1(Electrical conductivity)

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Engineering physics 1(Electrical conductivity)