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.

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 -148^oC.

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.

                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                        

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

                

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

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 18^th 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=Gm₁m_2/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 ε_0r*r

where (1/4π ε_0 = 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.