PHYSICS GALAXY
Monday 27 January 2014
Sunday 21 July 2013
VAN DE GRAAFF GENERATOR
VAN DE GRAAFF GENERATOR
In 1931, R.J. Van de Graaff designed an electrostatic
generator capable of generation very high potential of the order of 5×106
V, which was then made use in accelerating charged particles so as to carry out
nuclear reactions.
Principle
it is based on the following two electrostatic phenomena.
1. The
electric discharge takes place in air or gases readily at pointed conductors.
2. If a hollow
conductor is in contact with another conductor, then as charge is supplied to the conductor ,the hollow conductor continues accepting the charge irrecpective of the fact, howsoever large its potential may grow. The charge irrespective of the
fact, howsoever large its potential may grow. The charge immediately shifts to
outer surface the hollow conductor.
CONSTRUCTION AND WORKING
Van de Graff generator consists of a large hollow metallic
sphere C mounted on two insulation columns C1 C2 as shown in figure. An endless belt of an
insulating material is made to run on two pulleys P1 and P2
with the help of an electric motor. The metal comb B1, called spray
comb is held near the lower end of the belt.
When the spray comb is maintained at high positive potential
with the help of E.H.T. source, it produces ions in its vicinity. The positive
ions get sprayed on the belt due to the repulsive action of comb B2,
called collecting comb is positioned near the upper end of the belt, such that
the pointed ends touch the belt and the other end is in contact with the inner
surface of the metallic sphere S.
The comb B2
collects the positive ions and transfers them to the metallic sphere. The
charge transferred by the comb B2 immediately moves on to the outer
surface of the hollow sphere, as the belt goes on moving, the accumulation of
positive charge on the sphere also keeps on taking place continuously and its
potential rises considerably with the increase of charge on sphere its leakages
due to ionization of surrounding air also becomes faster, the maximum potential
to which the sphere can be raised is reached, when the rate of loss of charge due
to leakage becomes equal to the rate at which the charge is transferred to the
sphere.
To prevent the leakage of charge from the sphere the
generator is completely enclosed inside an earth connected steel tank, which is
filled with air under pressure. If the projectile such as protons, deutrons, is
now generated in the discharge tube D with lower end earthed and upper end
inside the hollow sphere, they get accelerated in downward direction along the
length of the tube, at the other end they come to hit the target with large
kinetic energy and bring about nuclear disintegration.
Van de Graff generator of this type was installed at the
Carnegie institute in Washington in 1937. One such generator was installed at
Indian Institute of technology in kanpur in 1970 and it accelerates particles
to 2 MeV energy.
Wednesday 10 July 2013
SUPER CONDUCTORS
SUPER- CONDUCTIVITY
Prof. K. Onnes in 1911, discovered
that certain metals and alloys at low temperature (-265 to -170 oC) lost their resistance considerably .this phenomenon is known as superconductivity
.
As the temperature decreases, the resistance
of material also decreases, but when the temperature reaches a certain critical
value called transition temperature the resistance of the material completely disappears
and it becomes zero.
Then the material behaves as if is a super
conductor and there will be flow of electrons without any resistance. The
critical temperature for the different materials is different.
Generally the critical temperature
for the mercury is -268.8 oC, and niobium at the critical
temperature -263.7 oC since last 25 years LOTS OF RESEARCH is going on this topic scientists are trying to make
such kind of alloys having high critical temp. Around -125 oC.
Examples of few alloy having the
critical temperature -128 oC Bi2Ca2Sr2Cu3O10
and Tl2Ca2Ba2Cu3O10 at
-148oC.
The cause of super conductivity is that
the free electrons in super conductor are no longer independent but some
mutually dependent and coherent when the critical temperature is reached.
The ionic vibration which could deflect
the free electron in metal is unable to deflect this coherent or cooperative
cloud of electrons in super conductors. It means the coherent cloud of
electrons makes no collision with ion of the super conductor and, as such there
is no resistance offered by the super conductor to the flow of electrons.
Applications of super conductors
1. Super
Conductors are used to produce very high speed computers.
2. Super
conductors are used for the transmission of electric power
3. Super
Conductors are used in making strong electro magnets.
Tuesday 11 June 2013
IMPORTANT TRICKS OF KINEMATICS
KINEMATICS TRICKS TO SLOVE THE NUMERICALS
v
Equations
of motions
v = u+at HERE v = final velocity
u = initial velocity
a= acceleration
s= displacement/ distance
S=ut+1/2at2
v2=u2+2as
v
When the object is falling downward the Equations
of motions having following form
v = u+gt HERE v = final velocity
u = initial velocity
g= gravitational acceleration
s= displacement/ distance
S=ut+1/2gt2
v2=u2+2gs
v
When
the object is ascending upward the Equations of motions having following form
v = u-gt HERE v = final velocity
u = initial velocity
g= gravitational acceleration
s= displacement/ distance
S=ut-1/2gt2
v2=u2-2gs
v
When
the object is dropped down toward the earth Equations of motions having
following form
v = gt HERE v = final velocity
u (initial velocity)=0
g= gravitational acceleration
s= displacement/ distance
S= 1/2gt2
v2= 2gs
v
The
formula for maximum height (h) attained by an object when it’s thrown upward
h=u2/2g
v
Time
taken by the object to attain the maximum height
t=u/g
v
Time
taken by the object to reach at the initial position from the maximum height
t=u/g
Friday 31 May 2013
A b c........... of physics
A b c........... of physics
A for acceleration
B for buoyancy
C for carnot cycle
D for diatomic
E for elasticity
F for friction
G for gravity
H for horizontal component
I for inertia
J for joule
K for kinetic energy
L for linear motion
M for moment
N for nautical miles
O for orientation
P for projectile motion
Q for qualitative
R for random errors
S for scalar quati.
T for torque
U for unit vector
V for viscocity
W for work
X for x ray
Y for yield strength
Z for zig-zag path
of physicsSSSSSSSSSSSSSSSSSSSS
This is alphabet for those students ,
who are
studying in class - xi
Saturday 25 May 2013
PHYSICAL WORLD
PHYSICAL WORLD AND MEASURMENT
What is a
science?
The word science originates from the Latin verb scientica , meaning “to
know”.
This knowledge which humans
have gained through observations and experiments , when organized
systematically is called science.
The science s which deal with non living things are called physical
sciences. Ex – Physics, Chemistry
The Scientific
Method And Theory
The scientific method involves following steps:-
1
Taking a large number of systematic observations through controlled
experiments.
2.
Studying these observations and looking for their logical behavior based on
quali
tative and qualitative reasoning.
3.
Mathematical modeling i.e. suggestion
some model to accent for the observed behavior.
4.
Theoretical prediction of what is not actually observed on the caulis of the
suggested model
Science is ever dynamic. There is no final theory in
science and no unquestioned authority amongst scientists.
What is a
Physics?
Physics is the branch so science
which is devoted to the study of nature and natural phenomena .
There are two
principal thrusts : Unification and Reduction.
Unification means attempting to explain diverse physical phenomena in
terms of a few concepts and laws .
Reductionism means attempting to derive the properties of a bigger , more
complex from the properties of its constituent simpler parts. The subject of
thermodynamics deals with bulk system in
terms macroscopic quantities like temperature , internal energy and entropy.
Scope and excitement of physics.
The two domains of interest in physics are : Macroscopic and
Microscopic
The Macroscopic domain of includes the study of phenomena involving objects
of finite size on terrestrial scale and even on astronomical scale .This make
up Classical Physics .
The Microscopic domain includes the study of phenomena
involving molecules , atoms, electrons and other elementary particles. This
makes up Modern physics.
Recently the domain intermediate between the
macroscopic domains has emerged .It involves the study of the a few tens of hundreds
of atoms of molecules .It is called Macroscopic Physics.
The classical physics includes subjects like Mechanics
, Thermodynamics ,Electrodynamics and optics.
PHYSICS RELATED
TO SOCIETY:-
Physics have
direct impact on society :
1. The
development of telephone , telex enable us to transmit messages instantly.
2. The
development of radio ,TV ,satellites , have revolutionized the means of communication
.
3. Advances
in electronics , computer , lasers , have greatly enriched the society.
4. Rapid
means of transport are no less important for the society .
5. Exploration
of the new sources of energy is of great significance to the society and so on
.
PHYSICS IN
RELATION TO TECHNOLOGY :
Technology is the application of the principles of
physics for practical purposes. For example – steam engine which played key
role in the industrial revolution in England in 18th century, was
developed on the laws of thermodynamics .
LINK BETWEEN
TECHNOLOGY AND PHYSICS:-
1.
|
STEAM ENGINE
|
LAWS OF THERMODYNAMICS
|
2.
|
ROCKET PROPULSION
|
NEWTONS LAWS OF MOTION
|
3.
|
AEROPLANE
|
BERNAULLIS
PRINCIPLE IN FLUID DYNAMICS
|
4.
|
SONAR
|
REFLECTION OF ULTRASONIC WAVES
|
5.
|
OPTICAL
FIBERS
|
TOTAL
INTERNAL REFLECTION
|
6.
|
ELECTRIC GENERATOR
|
RARADAYS LAWS OF ELECTROMAGNETIC INDUCTION
|
7.
|
HYDROELECTRIC
POWER
|
CONVERSION
OF GRAVITATIONAL POTENTIAL ENERGY INTO ELECTIRCAL ENERGY
|
8.
|
PARTICAL ASSELERATORS
|
MOTION OF CHARGED PARITICLES IN ELECTROMAGNATIC
FIELDS
|
9.
|
RADIO
AND T.V
|
GENERATION
, PROPAGATION AND DETECTION OF ELECROMAGNATIC WAVES
|
10.
|
PHOTOCELL
|
PHOTOELECTRIC EFFECT
|
11.
|
NUCLEAR
REACTOR
|
CONTROLLED
NUCLEAR CHAIN REACTION
|
12.
|
ELECTRON MICROSCOPE
|
WAVE NATURE OF ELECTRONS
|
13.
|
LASERS
|
LIGHT
AMPLIFICATION BY STIMULATED BY EMMISSION OF RADIATION
|
14
|
COMPUTERS
|
DIGITAL
LOGIC
|
SOME GREAT PHYSICSTS WITH THEIR COUNTRY
OR ORIGIN AND MAJOR
CONTRIBUTION / DISCOVERY
Name
|
Country
|
Major
contribution
|
Arachnids
|
Greece
|
Principle of buoyancy
|
Galileo gale lei
|
Italy
|
Law
of inertia
|
Sir is sac Newton
|
U.k.
|
Universal laws of gravitation and others
|
James clerk
maxwell
|
U.k
|
Electromagnetic
theory
|
J. J Thomson
|
U.k
|
Electron
|
W.k.
Roentgen
|
Germany
|
X-rays
|
Marie curie
|
Poland
|
Studies of natural radioactivity
|
Albert Einstein
|
Germany
|
Explanation
of photoelectric effect, relativity
|
R.a
millikan
|
Usa
|
Measurement of eletronic charge
|
Ernest
rutherford
|
New
zealand
|
Nuclear
model of atom
|
C.v. Raman
|
India
|
Inelastic scattering of light by molecules
|
M.n. Saha
|
India
|
Thermal
ionisation
|
S.n. Bose
|
India
|
Quantum statics
|
FUNDAMENTAL
FORCES IN NATURE :-
Force is an effort in the form of push or pull ,
required to move a body or stop a moving body of break body. Physics has
revealed that all the forces occurring in different contexts arise from a small
number of fundamental forces in nature . There are four fundamental forces.
a) Gravitational
forces c) Weak nuclear forces
b) Electromagnetic forces d) Strong nuclear forces
GRAVITATIONAL
FORCES:-
The
gravitational forces is the force of mutual attraction between any two
objects by virtue of their masses.
The magnitude of the force exerted by a partial of
mass m1 on another particle of mass m2 at a distance r
from it is given by Newton’s Law Of Gravitation:-
F=Gm1m2/r*r
Where G is universal gravitational content
and has the value G = 6.67×10-11 Nm2/Kg2
IMPORTANT
FATURE OF GRAVITATIONAL FORCES:-
1. Gravitational
Forces are universal attractive forces i.e.
they exist between microscopic as well as macroscopic objects respective of
their size, shape, separation, and intervening medium.
2. These
are the weakest forces in nature.
3. They
operate over very long distance especially when the bodies are massive . ex:- rotation
of earth around the sun is due to the gravitational pull of sun on earth.
4. Gravitational
forces are central forces .i.e. they act
along the line joining the centers of two bodies .
5. Gravitational
forces are central forces . i.e. they act along line joining the centers of two bodies.
6. Gravitational
forces are conservative forces.
7. The field particle of Gravitational forces is
called gravitation . The concept of exchange of field particle between two
bodies explains how the two bodies between from a distance.
WEAK NUCLEAR FORCES:
A) These
forces were discovered during the study of the phenomenon of β decays in
radioactivity.
B) The
energy emitted during β decays is shared by the β particles and antineutrino
.When antineutrino carries maximum energy , the energy of β particles is minimum and vice-versa .This particle was
later discovered experimentally.
THE WEAK
NUCLEAR forces are the forces of interaction between elementary particles of
short life time .
SOME IMPORTANT PROPERTIES OF THE WEAK NUCLEAR
FORCES :-
1.
THE WEAK NUCLEAR forces are 1025
times stronger than the gravitational forces.
2.
THE WEAK NUCLEAR forces exist
between leptons and leptons.
ELECTROMAGNETIC FORCES:-
The electromagnetic
forces are the forces between charged particles .
The change
in the motion produce magnetic effects and a magnetic field gives rise to a
force on a moving charge. That is why electric and magnetic forces , in general , are inseparable. Hence
the name electromagnetic forces .
The
magnitude of electrostatic force is F between two static point changes q1 and
q2 separated
by a distance r in air/vacuum
is given by coulombs law.
F= q1 q2/ 4π ε0r*r
where (1/4π ε0 = 9.0 x 109 N•m2/C2)
The smallest magnitude of charge found in nature
is the charge on an electron or a proton represented by e= 1.6 x 10-19
C
SALIENT
FEATURES OF ELECTROMAGNETIC FORCES:-
1.
These forces may be attractive or repulsive.
Like charges repel each other and unlike charges attract each other.
2.
These forces are governed by
Coulombs laws which are similar to Newton’s law of gravitation.
3.
Electrostatic forces are 1036
times stronger than gravitational forces between them, for any fixed distance.
4.
They operate over distances which
are not very large .
5.
They are central forces.
6.
They are also conservative forces.
7.
The field particles of
electromagnetic forces photon ,which carries no charge and has zero rest mass.
STRONG NUCLEAR FORCES:-
The forces
that bind the neutrons and protons together in a nucleus are called the STRONG
NUCLEAR FORCES .
SALIENT
FEATURES OF STRONG NUCLEAR
FORCES:-
1.
Nuclear forces are the strongest force in the nature. They are 1038
times stronger
than gravitational forces , 102 stronger than electrostatic forces and 1013 times stronger
than weak forces .
2.
Nuclear forces have the shortest range . They operate within the nuclear only .
3.
Nuclear forces donor depend on
charge on the nucleon.
4.
Nuclear forces onto obey inverse square law. They vary inversely as some
higher power of distance between nucleons.
5.
They are basically attractive forces.
6.
Nuclear forces are non central forces.
7.
They are also non- conservative forces.
8.
The field particles for nuclear forces Is the meson .
TOWARDS UNIFICATION OF FORCES:-
A lot of
efforts have been made towards unification of different forces and domains of
physics. Some of the highlights are:-
1.
In 1687 Newton unified terrestrial and celestial mechanics showing that
a the same laws of motion and the law of gravitation apply to both.
2.
Oersted and Faraday showed that electric and magnetic phenonema are
inseparable.
3.
Maxwell unified electricity magnetism and optics showing that light is
an electromagnetic wave.
Abus
salam and associates showed in 1979 that electromagnetic force and weak nuclear
force are different aspects of a single electroweak force . The predictions of
this theory were verities experimentally by Rubia et al in the year 1984.
NATURE OF PHYSICAL LAWS.:-
Some
special physical quantities remain constant in time . These are called the
conserved quantities of nature .
In
classical physics we often deal with the following conservation laws:
1.Law of conservation
of energy 2. Law of conservation of angular momentum
3. Law of
conservation linear momentum 4. Law
of conservation charge.
LAW OF CONSERVATION OF ENERGY:-
The sum
total of energy of all kinds in this universe remains constant .Energy can be transformed
from one form to the other or transported from one place to the other, but the
total amount of energy never changes.
LAW OF CONSERVATION LINEAR MOMENTUM :-
In the
absence of an external force , the linear momentum of a system remains
uncharged.
The law
means that in order to change the momentum of a system , we have to exert an
force on the system, the force or impulse must be exert on the system. This is because internal forces come in
balanced pairs that cancel within the object .To change he momentum , an
outside push of pull is requred . for example:-
1.
When a gun fired , force on the bullet inside the gun barrel is equla
oand opposite to the force on the gun. These forces are internal to the
momentum is 0. On firing the total
momintum of gum and bullet is still 0. On firing the bullet gains momintum in
the forward direction and the gun gains an equal momintum in the backward
direction so that the gun bullet sstem gains none. That is why the gum recoils
on firing.
LAW OF
CONSERVATION LINEAR MOMENTUM :-
Angular momentum (L) – Moment of
inertia(I) × Angular speed (ω)
If the total external torque acting on a system zero , angular momentum
to the system remains constant.
LAW OF CONSERVATION CHARGE
It means that charges in the (form of electrons) are neither reated nor
destroyed , but are simply transferred from one body to another.
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