Download NOTES ON LESSON ENGINEERING PHYSICS

NOTES ON LESSON
ENGINEERING PHYSICS - II
UNIT – I
CONDUCTING MATERIALS
Materials can be broadly classified in to three types based on conductivity.
They are,
1. Conductors (Example: metals),
Semi – conductors (Example: germanium, silicon) and
Insulators (Example: wood, mica, glass).
Conductivity of a Material:
Consider a solid material of length
and cross sectional area A. The no. of free
electrons in 1m3 of the solid is n. Total no. of electrons in the solid N is = Volume
no.of electrons.
Electron theory of metals.
Classical free electron theory.
Quantum free electron theory
Band theory
Drawbacks of Classical Free Electron Theory:
Contradiction occurs between classical and Quantum free electron theories on the
energy absorption of free electrons.
Wiedemann - Franz law (Lorentz Number)
The ratio of thermal conductivity to electrical conductivity of a metal is directly
proportional to the absolute temperature of the metal .
UNIT -II. SEMI CONDUCTING MATERIALS.
Introduction
The materials whose conductivity and resistivity lies in between conductors and insulators
are called semi - conducting materials.
They have almost filled valence and empty conduction bands.
They have small energy gap.
Based on the current conducting property there are two types of semi- conductors.
1) Intrinsic or pure semi- conductor
2) Extrinsic or impure semi – conductor
Carrier concentration in an intrinsic semiconductor:
Density of charge carries in an intrinsic semi conductor
Mobility and conductivity of intrinsic Semi- conductors
When and electric field is applied to a Semi- conductor, the charge carries attain drift
velocity
).
is proportional to the applied field E.
conducting materials.Also
is different for different Semi -
is different for different charge carriers.
Extrinsic Semi - Conductor:
It is in impure form.It is formed by doping impurities to an intrinsic Semi - Conductor.
Depending upon the type of impurity, there are two types of extrinsic Semi - Conductor.
N - type extrinsic Semi - Conductors and
P - type extrinsic Semi – Conductor
Hall effect:
When a current carrying conductor ( metal or Semi - conductor ) is placed in a transverse
magnetic field, an electric field is produced inside the conductor in a direction normal to
both the current and the magnetic field. This phenomen is calle Hall effect and the voltage
generated is called hall voltage .
UNIT - III
MAGNETIC & SUPER CONDUCTING MATERIALS
Introduction:
Super Conducting Phenomena
Super Conductivity was first observed in 1911 by the Dutch Physicist Heike
Kamerlingh onnes. In 1908, H.K onnes liquefied Helium gas at 4.2K. Also He
studied the properties of Hg. at very low temperatures. He found that at 4.2k, the
resistively of Hg suddenly becomes Zero (10-5 Ω cm)i.e., Hg becomes a super
conducting material.At very low temperature, the ordinary conducting material has
some receptivity.But the super conducting material has zero receptivity as shown in
figure.
UNIT IV
DIELECTRIC MATERIALS
Introduction
Dielectrics are insulators. They have no free electrons. At abnormal high
temperature, they allow a small current. They have high specific resistance ( ).
They have negative temperature co- efficient of resistance of resistance ( ). They
have large insulation resistance.
UNIT – V
MODERN ENGINEERING MATERIALS
INTRODUCTION
In the past few decades, all spheres of science and technology.Consequently,
sophisticated areas like aerospace, computers electronics communications require
new materials for their technological development.For this, right materials must be
selected.And proper application of those materials is essential.