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Introduction :Electronics :The branch of Engineering which deals with current
conduction through a vacuum, gas or semiconductor is known as
Electronics or Electronics is defined as a study of behaviour of
electron under different conditions of Externally applied fields.
Electronic Device :An electronic device is that in which current flows
through a vacuum or gas or semiconductor.
Atomic Structure :1. All the materials are composed of very small particles called
atoms.
2. An atom consists of a central nucleus of positive change
around which small negatively changed particles called
electrons revolve in different paths.
Nucleus :It is the central pact of an atom and contains protons
and neutrons.
 A proton is a positively changed particle, while the neutron
has the same mass as the proton, but has no change.
 Therefore nucleus of an atom is positively changed.
 The sum of protons and neutrons gives the entire weight of
an atom is called as atomic weight.
.
..
Atomic Weight = Number of protons + Number of neutrons
Extra nucleus :1. It is the outer pact of an atom and contains electrons only.
2. An electron is a negatively changed particle having negligible
mass.
3. The change of an electron is equal but opposite to that of a
proton.
4. Also the number of electrons is equal to the number of protons
in an atom under ordinary conditions. Therefore, an atom is
neutral as a whole.
5. The number of protons or electrons in an atom is called atomic
number.
(ie) Atomic number = Number of protons (or)
electrons in an atom.
1. The various orbits of an atom named as K, L, M, N…
2. The number of electrons in any orbit is given by
Ne = 2n2
Where,
Ne – Number of electrons.
n - Number of orbit;
(i) For Kth Shell (or for First orbit)
n=1
(ii) For Second orbit (or for L Shell)
n = 2;
(iii) For third orbit n = 3;
Energy Levels :1. Each orbit has fined amount of energy associated with it.
2. The electrons present in a particular orbit possess the
energy of that orbit.
3. The larger the orbit, the greater is its energy.
4. (ie) The outer orbit electron possess more energy than the
inner orbit electron.
5. The energy level of an electron increases with radius of an
orbit.
Valence Electrons : The Electrons in the outermost orbit of an atom are
known .
Valence Shell: The outermost orbit of an atom is called valence
orbit or valence shell.
The energy of an electron α Radius of the orbit.
R3
R2
R1
1. Valence Electrons) ie; the electrons present in an
outermost orbit have higher energy and are less tightly
bound to the atom than close orbit electron.
2. (ie) The force of attraction between the positively
changed proton and negatively changed
electron decreases with increase in distance (or)
Radius.
Force of attraction b/w electrons and protons
the nucleus (or) Radius of the
} α / distance from
1
Ionization:1. When an atom absorbs energy from a heat source or
from light source, the energy level of electrons are
raised.
2. We know that valence electrons posses more energy
and are less tightly bound with the atom, these
electrons will absorb external energy and escape
orbit it leaves vacant space.
3. Now the number of electrons is less than the number
of protons. Hence the atom is positively changed
and is called as a positive ion.
Negative Ion:Eg:- Hydrogen atom – H
1. When a neutral hydrogen atom loses its valence
electron and becomes a positive ion, it is designated
as H+.
2. The escaped valence electron is called free electron.
3. If free electron loses energy and falls in to the outer
shell of another neutral Hydrogen atom, the atom
becomes negatively changed and is called a negative
ion designated as H-.
The Electron :1. Since electrons deals with tiny particles called
electrons these small particles particles require
detailed study.
2. An electron is a negatively changed particle having
negligible mass.
Some of the important properties of an electron are
(i)
Change of an electron, e = 1.602x10-19
coulomb.
(ii)
Maas of an electron m= 9.0x10-31 Kg.
(iii)
Radius of an electron r = 1.9x10-15 metre.
3. The ratio e/m of am electron is 1.77x1011
coulombs/Kg. This means that mass of an electron
is very small as compared to its change.
Electron Volt (eV):A unit of work or energy, called the electron volt (eV).
1eV = 1.60x10-19 J
The name electron volt arises from the fact that, if an
electron falls through a potential of one volt, its kinetic energy will
increase by the decrease in potential energy.
eV = (1.60x10-19c) x (1V) = 1.60x10-19 J = 1eV ;
A force on a charged particles in an electric field :-
* The force on a unit positive change at any point in an
electric field is given by
fq = qε ; Where, q – change
ε – electric field Intensity
* In order to calculate the path of a changed in an
electric field, the force must be related to the mass and acceleration
of the particle by neuton’s second law of motion.
fq = qε = ma = m dv/dt
Where,
m= mass, Kg
a= acceleration, m/Sec2
v= Velocity, m/Sec
* The solution of this equation, subject to appropriate initial
conditions, gives the path of the particle.
* If the magnitude of the change on the electron is e, the
force on an electron in the field is
f = -eε
Note :The minus sign denotes that the force is in the direction
opposite to the field.
Potential :-
Potential difference across two parallel plates
The potential V (in Volts) of point Z with respect to
point Z0 is the work done against the field in taking a unit positive
charge from Z0 to Z
z
z
Thus V = - ∫ E . dz = - E(Z)
z0
z0
V = - E (Z – Z0)
V = - Ed ;
.
..
E = - V/d
Field Intensity :The electric field intensity is defined as the force on a
unit positive charge (or) the force on a unit positive charge at any
point in an electric field is the electric field intensity “E” at that
point.