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10+1 Physics Chapter – 1Physical World

Science:

The word science has been derived from a Latin word ‘Scientia’ which means ‘to know’. Hence science may be defined as the systematic study of facts events and happenings around us is called science.

Physics:

 The word physics has been derived from a Greek word ‘Fusis’ which means ‘Nature’. Hence physics may be defined as the branch of science, which deals with the study of nature and natural phenomena, is called physics.

Scientific Method:

To know fully about anything we have to follow the following four steps:1.   Systematic Observation
2.   Controlled experiments
3.   Studying and reasoning
4.   Mathematical modeling
5.   Theoretical Prediction and verification
The above steps taken together are known as Scientific Method.

Scientific Theory:

A set of minimum number of laws which can explain the behavior of physical phenomena is known as scientific theory.

Unification:

The effort to explain diverse physical phenomena in terms of a few concepts and laws is known as unification. 

E.g. many physical phenomena like fall of an apple to the ground, motion of planet around the sun etc. are described by the same law of Gravitation (Newton’s Law of Gravitation)

Progress in Unification of Different Forces

Physicist	Year	Achievement in Unification
Isaac Newton	1687	Unified celestial and terrestrial mechanics. Showed that the same laws of motion and the law of gravitation apply to both the domains.
Hans Christian Oersted Michael Faraday	1820 1830	Unified electricity, magnetism and optics by showing light is an electromagnetic wave.
Sheldon Glashow Abdus Salam Steven Weinberg	1979	Showed that the weak nuclear force and the electron agnatic force could be viewed as different aspects of a single electro-weak force
Carlo Rubia Simon Vander Meer	1984	Experimental verification of the theory of electro- weak force.

Reductionism:

An effort to derive the properties of a bigger or more complex system from the properties of its constituent simpler parts is known as reductionism.

E.g. the subject of thermodynamics is explained by many terms and quantities like temperature, internal energy, entropy etc.

Scope of Physics:

The scope of physics is wide, covering a tremendous range of magnitude of physical quantities. e.g·         Range of length in physics is from 10^-14m (radius of nucleus) to 10²⁶m (length of Galaxy.) Hence ratio of measurement is in order of 10⁴⁰.
·         Range of measurement of time is 10^-22 s to 10¹⁸ s.
·         Range of mass is from 10^–30 kg (mass of an electron) to 10⁵⁵ kg (mass of Galaxy).

Excitements of Physics:

The study of Physics is exciting in many ways for example-·         Use of robots
·         Journey to nearby planets with controls from the ground
·         Means of communication like cellular phone, internet etc.
·         Exploring the new sources of energy etc is really exciting in physics.

Physics, Technology and Society:

Physics and technology are related to each other, Sometimes technology gives rise to new physics; at other times physics generates new technology. Both have direct impact on society.

Some Great Physicist and Their Contributions:

Name	Major contribution/discovery	Country of Origin
Archimedes	Principle of buoyancy; Principle of the lever	Greece
Galileo Galilei	Law of inertia	Italy
Christiaan Huygens	Wave theory of light	Holland
Isaac Newton	Universal law of gravitation; Laws of motion; Reflecting telescope	U.K.
Michael Faraday	Laws of electromagnetic induction	U.K.
James Clerk Maxwell	Electromagnetic theory; Light-an electromagnetic wave	U.K.
Heinrich Rudolf Hertz	Generation of electromagnetic waves	Germany
J.C. Bose	Ultra  short radio waves	India
W.K. Roentgen	X-rays	Germany
J.J. Thomson	Electron	U.K.
Marie Sklodowska Curie	Discovery of radium and polonium; Studies on natural radioactivity	Poland
Albert Einstein	Explanation of photoelectric effect; Theory of relativity	Germany
Name	Major contribution/discovery	Country of Origin
Victor Francis Hess	Cosmic radiation	Austria
R.A. Millikan	Measurement of electronic charge	U.S.A.
Ernest Rutherford	Nuclear model of atom	New Zealand
Niels Bohr	Quantum model of hydrogen atom	Denmark
C.V. Raman	Inelastic scattering of light by molecules	India
Louis Victor de Borglie	Wave nature of matter	France
M.N. Saha	Thermal ionization	India
S.N. Bose	Quantum statistics	India
Wolfgang Pauli	Exclusion principle	Austria
Enrico Fermi	Controlled nuclear fission	Italy
Werner Heisenberg	Quantum mechanics; Uncertainty principle	Germany
Paul Dirac	Relativistic theory of electron; Quantum statistics	U.K.
Edwin Hubble	Expanding universe	U.S.A.
Ernest Orlando Lawrence	Cyclotron	U.S.A.
James Chadwick	Neutron	U.K.
Hideki Yukawa	Theory of nuclear forces	Japan
Homi Jehangir Bhabha	Cascade process of cosmic radiation	India
Lev Davidovich Landau	Theory of condensed matter; Liquid helium	Russia
S. Chandrasekhar	Chandrasekhar limit, structure and evolution of stars	India
John Bardeen	Transistors; Theory of super conductivity	U.S.A.
C.H. Townes	Maser; Laser	U.S.A.
Abdus Salam	Unification of weak and electromagnetic interactions	Pakistan

Link between Technology and Physics

Technology	Scientific principle(s)
Steam engine	Laws of thermodynamics
Nuclear reactor	Controlled nuclear fission
Radio and Television	Generation, propagation and detection of electromagnetic waves
Computers	Digital logic
Lasers	Light amplification by stimulated emission of radiation
Production of ultra high magnetic fields	Superconductivity
Rocket propulsion	Newton’s laws of motion
Electric generator	Faraday’s laws of electromagnetic induction
Hydroelectric power	Conversion of gravitational potential energy into electrical energy
Aero plane	Bernoulli’s principle in fluid dynamics
Particle accelerators	Motion of charged particles in electromagnetic fields
Sonar	Reflection of ultrasonic waves
Optical fibers	Total internal reflection of  light
Non-reflecting coatings	Thin film optical interference
Electron microscope	Wave nature of electrons
Photocell	Photoelectric effect
Fusion test reactor (Tokamak)	Magnetic confinement of plasma
Giant Metrewave Radio Telescope (GMRT)	Detection of cosmic radio waves
Bose-Einstein condensate	Trapping and cooling of atoms by laser beams and magnetic fields.

Fundamental forces in Nature:

There are four fundamental forces in Nature:
1.   Gravitational Force
2.   Weak nuclear Force
3.   Electromagnetic Force
4.   Strong nuclear Force

 1.    Gravitational Force:

The gravitational force is the force of mutual attraction between any two bodies in the universe by virtue of their masses.

If m₁ and m₂ are the masses of two bodies separated by distance r then gravitational force between them is given by

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Properties of Gravitational forces:

1.   Gravitational forces are universal attractive forces in nature.
2.   They operate over very long distances and do not require any intervening medium.
3.   They obey inverse square law.
4.   They are central forces.
5.   They are conservative forces.
6.   They are weakest force in nature, but it plays a key role in the large scale phenomena of universe such as formation and evolution of stars, galaxies etc. in nature.
7.   The field particle of gravitational forces is ‘graviton’

2.    Weak nuclear Forces:

The weak nuclear force appears only in certain nuclear processes such as the β-decay of a nucleus. In β-decay, the nucleus emits an electron and an uncharged particle called neutrino.

Properties of weak Nuclear Forces:

1.   The weak nuclear force is not as weak as the gravitational force, but much weaker than the strong nuclear and electromagnetic forces.

2.   The range of weak nuclear force is exceedingly small, of the order of 10-16 m.

3.    Electromagnetic Force

Electromagnetic force is the force between charged particles. In the simpler case when charges are at rest, the force is given by Coulomb’s law: attractive for unlike charges and repulsive for like charges. Charges in motion produce magnetic effects and a magnetic field gives rise to a force on a moving charge. Electric and magnetic effects are, in general, inseparable – hence the name electromagnetic force.

Properties of Electromagnetic Forces:

1.   Like the gravitational force, electromagnetic force acts over large distances and does not need any intervening medium.

2.   It is enormously strong compared to gravitational force.

3.   It may be attractive or repulsive.

4.    Strong Nuclear Forces:

The forces that bind the neutrons and protons together in a nucleus are called the strong nuclear forces.

Properties of Strong Nuclear Forces:

1.    Nuclear forces are the strongest forces in nature.
2.    Nuclear forces have the shortest range.
3.    They don’t obey inverse square law.
4.    They don’t depend on charge of particles.
5.    They are non-conservative and non-central forces.
6.    The field particle for the nuclear forces is the π-meson.

Summary of the fundamental forces in nature:

Name	Relative strength	Range	Operates among
Gravitational force	10–39	Infinite	All objects in the  universe
Weak  nuclear force	10–13	Very short, Sub-nuclear size (~10–16m)	Some elementary particles, particularly electron and neutrino
Electromagnetic  force	10–2	Infinite	Charged particles
Strong  nuclear force	1	Short, nuclear size (~10–15m)	Nucleons, heavier elementary particles

Nature of Physical Laws

Conservation Laws:

Conserved Quantities: The physical quantities that remain unchanged with time are called conserved quantities.

Conservation: conservation of some physical quantity means that the quantity does not change with time.

The laws of conservation play an important and basic role in physics. These laws are as under:

1.    Law of Conservation of Energy:
The amount of total energy in the universe remains constant. Energy can neither be created nor be destroyed; it can just be converted from one form to the other.
2.    Law of Conservation of Charge:
During any process taking place in an electrically isolated system, the algebraic sum of the charges always remains constant.
3.    Law of Conservation of Linear Momentum:
If the resultant external force on a system is zero, the total linear momentum of the system remains constant.
4.    Law of Conservation of Angular Momentum:
If the resultant external torque acting on a system is zero, the total angular momentum of the system remains constant.

Note:

In Physics, studies are carried out of space and time. In classical mechanics space and time are considered independent of each other while according to the theory of relativity given by Einstein, space and time are interrelated.

Basic Reason Behind Conservation Laws:

• ·   Space is homogeneous and isotropic, as a result of this; we have the law of conservation of linear momentum and the law of conservation of angular momentum.
• ·     Time is also homogeneous and isotropic. Because of homogeneity of time we have the law of conservation of energy. But till today physicists are unable to know, what will be the possible result due to isotropicity of time.  
• ·       Basic reasons behind the existence of laws of conservation of charge are still not known. The great theoretical physicist of 20th century, Dirac was of the opinion that, the law of conservation of charge may be due to isotropic nature of time.

EXERCISES

Choose the correct option from the given options: 1.    .......... are two fundamental constituents of universe.
(A)         Matter and radiation
(B)         Heat and light
(C)         Molecule and atom
(D)         Electron and proton.

2.    “The most incomprehensible thing about the world is that it is comprehensible.” This statement is given by –
(A)         Einstein
(B)         Chadwick
(C)         Bohar
(D)         Newton

3.    .......... is the fourth state of matter.
(A)         Solid
(B)         Liquid
(C)         Gas
(D)         Plasma


4.    Nucleus of molecule is made up of which fundamental constituents?
(A)         Electron and proton
(B)         Electron and neutron
(C)         Proton and neutron
(D)         only electron

5.    An Indian physicist who received Noble Prize is-
(A)         H.J. Bhaba
(B)         C.V. Raman
(C)         J.C. Bose
(D)         None of these

6.    S. Chander Shekhar, an Indian born American scientist was awarded Noble Prize for his contribution in the field of:
(A)         Biophysics
(B)         Optics
(C)         Astronomy
(D)         Superconductivity

7.    What is a acronym of ECG?
(A)         Electron cardiogram
(B)         Electron colour graph
(C)         Electro cardiograph
(D)         Electric cordiogram

8.    What is full form of NMR?
(A)         Neutron Magnetic Resonance
(B)         Nuclear Magnetic Resonance
(C)         Neutrino Magnetic Resonance
(D)         Nuclear Motion Resonance

9.    What is full form of ESR?
(A)         Electric Spin Resonance
(B)         Electron Spin Resonance
(C)         Electron Spin Radar
(D)         Electric Space Radar


10.  The force exerting between neutron and proton within the nucleus is the
(A)         Gravitational force
(B)         Electromagnetic force
(C)         Strong nuclear force
(D)         Weak nuclear force

11.  Who discovered neutron?
(A)         J.J. Thomson
(B)         James Routherford
(C)         Chadwick
(D)         Nils Bohr

12.  Wireless telegraphy was invented by –
(A)         Marconi
(B)         Chadwick
(C)         Newton
(D)         Hertz

13.  Which particles are emitted during the β-decay from the nucleus?
(A)         Neutron and proton
(B)         Electron and proton
(C)         Electron and neutron
(D)         Electron and neutrino

14.  Space is isotropic. Which law of conservation is the result of this?
(A)         Law of conservation of energy
(B)         Law of conservation of charge
(C)         Law of conservation of linear momentum
(D)         Law of conservation of angular momentum

15.  Space is homogenous. Which law of conservation is the result of this?
(A)         Law of conservation of energy.
(B)         Law of conservation of charge
(C)         Law of conservation of linear momentum.
(D)         Law of conservation of angular momentum



16.  Time is homogeneous. Which law of conservation is the result of this?
(A)         Law of conservation of energy
(B)         Law of conservation of charge
(C)         Law of conservation of linear momentum
(D)         Law of conservation of angular momentum

17.  The basic reason behind existence of which conservation of law is still not known?
(A)         Law of conservation of energy.
(B)         Law of conservation of charge.
(C)         Law of conservation of linear momentum.
(D)         Law of conservation of angular momentum.  

18. Einstein was awarded Noble prize for:
(A)         Theory of relativity
(B)         Photoelectric effect
(C)         Principle of inertia
(D)         None of above 

19.  The range of physics is about ......(A) Zero to infinite         (B) range of nucleus      (C) Earth to sun       (D) near around the earth

20.  Physics considered vacuum as one  ......(A)     Physical Quantity    (B)      Physical State          (C)     Physical unit            (D)     Infinite

21.   ...... is a branch of physics related to charge and magnetic field.(A)     Mechanics               (B)         Electrodynamics       (C)         Thermodynamics   
(D)         Optics



22.   Electromagnetic force is ......
(A)    only attractive                                                 (B)         Attractive and repulsive(C)      Only repulsive                                                 (D)      Short range force

23.   If the resultant external ...... acting on the system is zero, total linear momentum of the system remains constant.

(A)  Force                       

(B) Torque                     

(C)    Charge                   

(D)    Mass

Answer Key

1	2	3	4	5	6	7	8	9	10
A	A	D	C	B	C	C	B	B	C
11	12	13	14	15	16	17	18	19	20
C	A	D	D	C	A	B	B	A	B
21	22	23
B	B	A

Homogeneity of Space: No point is space is special, so the same basic laws of physics should govern all of space. For instance, if electrons repel each other on Earth, we don't expect electrons to attract each other in the Andromeda Galaxy. More generally, if Maxwells equations hold on Earth, we also assume that they hold in the rest of the universe.

Homogeneity of Time: No point in time is special, so the same basic laws of physics should govern all of time. So again, if Maxwells equations are valid today, there is no reason to expect the equations to suddenly become invalid tomorrow.

Isotropy of Time: No direction in time is special. One way to visualize this is to look at a simulation of Brownian motion for a classical gas at equilibrium, and then run the video in reverse -- the particles behave in the exact same way!