Ncert Physics Book

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CONTENTS FOREWORD PREFACE A eminence FOR THE TEACHER CHAPTER iii v x 1 tangible beingness 1. 1 1. 2 1. 3 1. 4 1. 5 What is physical science ? area and excitement of physics Physics, technology and society primordial thrusts in personality Nature of absolute-arm honors CHAPTER 1 2 5 6 10 2 UNITS AND MEASUREMENTS 2. 1 2. 2 2. 3 2. 4 2. 5 2. 6 2. 7 2. 8 2. 9 2. 10 inception The international administration of units Measurement of length Measurement of massMeasurement of time Accuracy, precision of instruments and errors in measuring Significant figures Dimensions of physical quantities Dimensional formulae and dimensional equations Dimensional psychoanalysis and its applications CHAPTER 16 16 18 21 22 22 27 31 31 32 3 MOTION IN A dead on target LINE 3. 1 3. 2 3. 3 3. 4 3. 5 3. 6 3. 7 commitment Position, path length and displacement Average belt a doggeding and average cannonb solely along Instantaneous speed and speed Acceleration Kinematic equations for wish wellly accelerated dubiousness copulation velocity CHAPTER 39 39 42 43 45 47 51 4 MOTION IN A PLANE 4. 1 4. 2 4. 3 4. 4 4. 5 IntroductionScalars and vectors Multiplication of vectors by real numbers Addition and subtraction of vectors in writing(p) method Resolution of vectors 65 65 67 67 69 CK xii 4. 6 4. 7 4. 8 4. 9 4. 10 4. 11 Vector attachment analytical method Motion in a plane Motion in a plane with perpetual quickening Relative velocity in two dimensions Projectile apparent movement analogous round executi on CHAPTER 71 72 75 76 77 79 5 LAWS OF MOTION 5. 1 5. 2 5. 3 5. 4 5. 5 5. 6 5. 7 5. 8 5. 9 5. 10 5. 11 Introduction Aristotles f everyacy The law of inertia delinquent norths first law of action Newtons second law of consummation Newtons third law of motion preservation of impulse symmetricalness of a particle Common depicts in mechanism Circular motion Solving problems in mechanics CHAPTER 89 90 90 91 93 96 98 99 100 104 105 6 WORK, ENERGY AND POWER 6. 1 6. 2 6. 3 6. 4 6. 5 6. 6 6. 7 6. 8 6. 9 6. 10 6. 11 6. 12 Introduction Notions of work and energizing button The work- button theorem Work Kinetic nix Work d sensation by a variable force The work- aught theorem for a variable force The concept of potential competency The conservation of mechanical energy The potential energy of a terpsichore Various forms of energy the law of conservation of energy Power Collisions CHAPTER 114 116 116 117 118 119 120 121 123 126 28 129 7 SYSTEM OF PARTICLES AND ROTATIONAL MOTION 7. 1 7. 2 7. 3 7. 4 7. 5 7. 6 7. 7 7. 8 7. 9 7. 10 Introduction Centre of mass Motion of centre of mass Linear momentum of a system of particles Vector product of two vectors angu spic-and-span velocity and its relation with linear velocity Torque and angular momentum Equilibrium of a rigid body Moment of inertia Theorems of perpendicular and line of latitude axes 141 144 148 149 150 152 154 158 163 164 CK bakers dozen 7. 11 7. 12 7. 13 7. 14 Kinematics of rotational motion closely a fixed axis dynamics of rotational motion ab egress a fixed axis Angular momentum in case of rotations about a fixed axisRolling motion CHAPTER 167 169 171 173 8 GRAVITATION 8. 1 8. 2 8. 3 8. 4 8. 5 8. 6 8. 7 8. 8 8. 9 8. 10 8. 11 8. 12 Introduction Keplers laws Universal law of gravitation The gravitative constant Acceleration due to gravitation of the existencely concern Acceleration due to dryness below and above the surface of earth Gravitational potential energy Escape speed Earth satellite ef ficacy of an orbiting satellite fixed and polar satellites Weightlessness 183 184 185 189 189 190 191 193 194 195 196 197 APPENDICES 203 ANSWERS 219 CK CK CONTENTS FOREWORD PREFACE A NOTE FOR THE TEACHERS CHAPTER iii vii x 9 MECHANICAL PROPERTIES OF SOLIDS 9. 9. 2 9. 3 9. 4 9. 5 9. 6 9. 7 Introduction elastic band behaviour of solids Stress and strain Hookes law Stress-strain curve expansile moduli Applications of elastic behaviour of materials CHAPTER 231 232 232 234 234 235 240 10 MECHANICAL PROPERTIES OF FLUIDS 10. 1 10. 2 10. 3 10. 4 10. 5 10. 6 10. 7 Introduction Pressure contour flow Bernoullis principle Viscosity Reynolds number Surface strain CHAPTER 246 246 253 254 258 260 261 11 THERMAL PROPERTIES OF MATTER 11. 1 11. 2 11. 3 11. 4 11. 5 11. 6 11. 7 11. 8 11. 9 11. 10 Introduction Temperature and heat Measurement of temperature Ideal- grease-gun equation and absolute temperaturethermic expansion finespun heat capacity Calorimetry Change of state Heat transfer Newton s law of cool CHAPTER 274 274 275 275 276 280 281 282 286 290 12 THERMODYNAMICS 12. 1 12. 2 Introduction thermal equilibrium 298 299 CK CK xii 12. 3 12. 4 12. 5 12. 6 12. 7 12. 8 12. 9 12. 10 12. 11 12. 12 12. 13 ordinal law of thermodynamics Heat, internal energy and work First law of thermodynamics Specific heat capacity thermodynamic state variables and equation of state Thermodynamic processes Heat locomotive locomotives Refrigerators and heat pumps Second law of thermodynamics Reversible and irreversible processes Carnot engine CHAPTER 300 300 302 03 304 305 308 308 309 310 311 13 KINETIC THEORY 13. 1 13. 2 13. 3 13. 4 13. 5 13. 6 13. 7 Introduction molecular(a)(a) character of matter Behaviour of gaseous statees Kinetic conjecture of an ideal gas Law of equipartition of energy Specific heat capacity Mean free path CHAPTER 318 318 320 323 327 328 330 14 OSCILLATIONS 14. 1 14. 2 14. 3 14. 4 14. 5 14. 6 14. 7 14. 8 14. 9 14. 10 Introduction triennial and oscilatory motion s Simple charitable motion Simple harmonic motion and uniform circular motion Velocity and acceleration in easy harmonic motion military law for simple harmonic motion Energy in simple harmonic motion Some systems executing SHMDamped simple harmonic motion Forced oscillations and resonance CHAPTER 336 337 339 341 343 345 346 347 351 353 15 WAVES 15. 1 15. 2 15. 3 15. 4 15. 5 15. 6 Introduction Transverse and longitudinal waves Displacement relation in a progressive wave The speed of a travelling wave The principle of superposition of waves Reflection of waves 363 365 367 369 373 374 CK CK xiii 15. 7 15. 8 Beats Doppler effect 379 381 ANSWERS 391 BIBLIOGRAPHY 401 INDEX 403 CK CHAPTER ONE physiologic populace 1. 1 WHAT IS PHYSICS ? 1. 1 What is physics ? 1. 2 stage setting and excitement of physics 1. 3 Physics, technology and society 1. 4 Fundamental forces in nature 1. Nature of physical laws Summary Exercises Humans cede always been curious about the area some them. The n ight fling with its bright ethereal discourageminations has fascinated gentlemans gentlemans since time immemorial. The regular repetitions of the twenty-four hour period and night, the annual cycle of seasons, the eclipses, the tides, the volcanoes, the rainbow bedevil always been a source of wonder. The world has an astonishing variety of materials and a bewildering diversity of life history and behaviour. The inquiring and fanciful kind mind has responded to the wonder and awe of nature in contrary ways. whizz kind of response from the ear craftst time has been to ob practice the hysical surround carefully, look for any meaningful patterns and relations in natural phenomena, and arrive at and utilise tonic tools to interact with nature. This human endeavour led, in melt of time, to modern science and technology. The word Science originates from the Latin verb Scientia meaning to lie with. The Sanskrit word Vijnan and the Arabic word Ilm c onvey similar meaning, namely fellowship. Science, in a broad sense, is as old as human species. The early civilisations of Egypt, India, China, Greece, Mesopotamia and umpteen another(prenominal)(a)s made vital contributions to its progress. From the sixteenth century onwards, corking strides were made n science in Europe. By the middle of the twentieth century, science had become a truly international enterprise, with many cultures and countries add to its rapid growth. What is Science and what is the so-called Scientific Method ? Science is a systematic attempt to understand natural phenomena in as more than(prenominal) detail and depth as possible, and use the knowledge so gained to expect, deepen and control phenomena. Science is exploring, sampleing and predicting from what we see around us. The curiosity to learn about the world, unravelling the secrets of nature is the first step towards the husking of science.The scientific method involves some(prenominal)(prenominal) interconnec ted steps Systematic postings, controlled experiments, qualitative and 2 quantitative intellectualing, mathematical role puzzleling, prediction and verification or falsification of theories. Speculation and conjecture withal pass on a place in science but ultimately, a scientific guess, to be acceptable, must be verified by applicable placards or experiments. There is much philosophical debate about the nature and method of science that we need not discuss here. The interplay of supposition and observation (or experiment) is unsounded to the progress of science. Science is ever dynamic.There is no final system in science and no unquestioned authority among scientists. As observations change in detail and precision or experiments yield new results, theories must account for them, if necessary, by introducing modifications. Somemultiplication the modifications may not be forceful and may lie within the digitwork of existing conjecture. For specimen, when Johannes Kepler (1571-1630) examined the extensive info on planetary motion collected by Tycho Brahe (1546-1601), the planetary circular orbits in heliocentric theory (sun at the centre of the solar system) imagined by Nicolas Copernicus (14731543) had to be replaced by elliptical rbits to fit the selective information better. Occasionally, however, the existing theory is simply unable to explain new observations. This causes a major fervor in science. In the beginning of the twentieth century, it was realised that Newtonian mechanics, trough then a very successful theory, could not explain nearly of the most basic features of atomic phenomena. Similarly, the then accepted wave estimate of conflagrate failed to explain the photoelectric effect properly. This led to the development of a radically new theory (Quantum Mechanics) to deal with atomic and molecular phenomena. effective as a new experiment may suggest an lternative theory-based model, a theoretical advance may suggest what to look for in well-nigh experiments. The result of experiment of diffusion of alpha particles by silver foil, in 1911 by Ernest Rutherford (18711937) established the atomic model of the atom, which then became the derriere of the quantum theory of hydrogen atom given in 1913 by Niels Bohr (18851962). On the other hand, the concept of antiparticle was first introduced theoretically by Paul Dirac (19021984) in 1930 and confirmed two years later on by the experimental scuppery of positron (antielectron) by Carl Anderson. P HYSICS Physics is a basic purify in the category f Natural Sciences, which as well includes other disciplines interchangeable Chemistry and Biology. The word Physics comes from a Greek word meaning nature. Its Sanskrit equivalent is Bhautiki that is used to refer to the study of the physical world. A precise definition of this discipline is neither possible nor necessary. We can broadly expound physics as a study of the basic laws of nature and their ve rbalism in antithetical natural phenomena. The scope of physics is exposit presently in the next section. Here we remark on two tip thrusts in physics join and reduction. In Physics, we attempt to explain some(prenominal)(prenominal)(a) hysical phenomena in terms of a some concepts and laws. The endeavour is to see the physical world as manifestation of some universal laws in diametric realms and conditions. For example, the said(prenominal) law of gravitation (given by Newton) describes the fall of an apple to the ground, the motion of the moon around the earth and the motion of planets around the sun. Similarly, the basic laws of electromagnetism (Maxwells equations) g everywheren all electric and magnetized phenomena. The attempts to commingle primordial forces of nature (section 1. 4) reflect this same quest for unification. A related effort is to derive the properties of a igger, much complex, system from the properties and native interactions of its constit uent simpler part. This approach is called reductionism and is at the heart of physics. For example, the subject of thermodynamics, developed in the nineteenth century, deals with bulk systems in terms of macroscopical quantities such as temperature, internal energy, entropy, etc. Subsequently, the subjects of kinetic theory and statistical mechanics interpreted these quantities in terms of the properties of the molecular constituents of the bulk system. In particular, the temperature was seen to be related to the average kinetic energy of molecules of the system. . 2 SCOPE AND EXCITEMENT OF PHYSICS We can get some idea of the scope of physics by looking at its versatile sub-disciplines. Basically, on that point are two domains of interest macroscopic and microscopic. The macroscopic domain includes phenomena at the laboratory, terrestrial and astronomical scurfs. The microscopic domain includes atomic, molecular and atomic P HYSICAL WORLD phenomena*. Classical Physics deals in the main with macroscopic phenomena and includes subjects interchangeable Mechanics, Electrodynamics, Optics a nd T hermodynamics . Mechanics founded on Newtons laws of motion and the law of gravitation is concerned with the motion (or quilibrium) of particles, rigid and deformable bodies, and frequent systems of particles. The propulsion of a rocket by a jet of ejecting gases, elongation of water waves or sound waves in air, the equilibrium of a bended rod under a load, etc. , are problems of mechanics. Electrodynamics deals with electric and magnetised phenomena associated with supercharged and magnetized bodies. Its basic laws were given by Coulomb, Oersted, Fig. 1. 1 chemic process, etc. , are problems of interest in thermodynamics. The microscopic domain of physics deals with the constitution and structure of matter at the minute scales of atoms and nuclei (and even ower scales of length) and their interaction with contrastive probes such as electrons, photons an d other dewy-eyed particles. Classical physics is inadequate to handle this domain and Quantum surmise is currently accepted as the proper framework for explaining microscopic phenomena. Overall, the edifice of physics is beautiful and bossy and you will appreciate it much as you pursue the subject. Theory and experiment go hand in hand in physics and help each others progress. The alpha scattering experiments of Rutherford gave the nuclear model of the atom. Ampere and Faraday, and encapsulated by Maxwell in his famous set of equations.The motion of a current-carrying conductor in a magnetized field, the response of a circuit to an ac voltage (signal), the working of an antenna, the filename extension of radio waves in the ionosphere, etc. , are problems of electrodynamics. Optics deals with the phenomena involving light. The working of telescopes and microscopes, colours exhibited by thin films, etc. , are topics in optics. Thermodynamics, in contrast to mechanics, does not deal with the motion of bodies as a whole. Rather, it deals with systems in macroscopic equilibrium and is concerned with changes in internal energy, temperature, entropy, etc. , of the ystem through external work and transfer of heat. The efficiency of heat engines and refrigerators, the direction of a physical or * 3 You can now see that the scope of physics is truly vast. It covers a terrific range of magnitude of physical quantities similar length, mass, time, energy, etc. At one end, it studies phenomena at the very midget scale of length -14 (10 m or even less) involving electrons, protons, etc. at the other end, it deals with astronomical phenomena at the scale of galaxies or even the entire creation whose extent is of the order of 26 10 m. The two length scales differ by a factor out of 40 10 or even more.The range of time scales can be obtained by dividing the length scales by the 22 speed of light 10 s to 1018 s. The range of masses goes from, say, 1030 kg (mass o f an 55 electron) to 10 kg (mass of cognise observable origination). Terrestrial phenomena lie somewhere in the middle of this range. Recently, the domain intermediate mingled with the macroscopic and the microscopic (the so-called mesoscopic physics), dealing with a few tens or hundreds of atoms, has emerged as an exciting field of research. 4 Physics is exciting in many ways. To some people the excitement comes from the elegance and universality of its basic theories, from the fact that few basic concepts and laws can explain phenomena covering a boastfully range of magnitude of physical quantities. To some others, the challenge in carrying out imaginative new experiments to unlock the secrets of nature, to verify or refute theories, is thrilling. use physics is equally demanding. Application and exploitation of physical laws to make reusable devices is the most interesting and exciting part and requires great ingenuity and exertion of effort. What lies behind the phenomenal progress of physics in the last few centuries? Great progress usually accompanies changes in our basic perceptions.First, it was realised that for scientific progress, moreover qualitative thinking, though no doubt of import, is not enough. vicenary measurement is central to the growth of science, e particular(a)ly physics, because the laws of nature happen to be expressible in precise mathematical equations. The second most important insight was that the basic laws of physics are universal the same laws guard in widely different contexts. Lastly, the strategy of approximation turned out to be very successful. Most observed phenomena in workaday life are rather complicate manifestations of the basic laws. Scientists recognised the importance f extracting the essential features of a phenomenon from its less fundamental aspects. It is not practical to take into account all the complexities of a phenomenon in one go. A grievous strategy is to focus first on the essential feat ures, discover the basic principles and then introduce corrections to build a more sensitive theory of the phenomenon. For example, a stone and a feather dropped from the same whirligig do not reach the ground at the same time. The reason is that the essential aspect of the phenomenon, namely free fall under gravity, is complicated by the presence of air exemption. To get the law of free all under gravity, it is better to create a situation wherein the air resistance is negligible. We can, for example, let the stone and the feather fall through a long evacuated tube. In that case, the two objects will fall almost at the same rate, giving the basic law that acceleration due to gravity is free-living of the mass of the object. With the basic law thus found, we can go confirm to the feather, introduce corrections due to air resistance, modify the existing theory and try to build a more realistic P HYSICS Hypothesis, axioms and models One should not think that everything can be pro ved with physics and mathematics. on the whole physics, and as well as mathematics, is based on assumptions, each of which is variously called a hypothesis or axiom or postulate, etc. For example, the universal law of gravitation proposed by Newton is an assumption or hypothesis, which he proposed out of his ingenuity. Before him, there were several observations, experiments and data, on the motion of planets around the sun, motion of the moon around the earth, pendulums, bodies falling towards the earth etc. Each of these required a recognize explanation, which was more or less qualitative. What the universal law of gravitation says is that, if we encounter that any two odies in the universe attract each other with a force proportional to the product of their masses and inversely proportional to the square of the distance between them, then we can explain all these observations in one stroke. It not only explains these phenomena, it also allows us to predict the results of futur e experiments. A hypothesis is a supposition without assuming that it is true. It would not be fair to ask anybody to prove the universal law of gravitation, because it cannot be proved. It can be verified and substantiated by experiments and observations. An axiom is a self-evident truth while a model s a theory proposed to explain observed phenomena. But you need not worry at this stage about the nuances in using these words. For example, next year you will learn about Bohrs model of hydrogen atom, in which Bohr take for granted that an electron in the hydrogen atom follows certain rules (postutates). Why did he do that? There was a large amount of spectroscopic data onwards him which no other theory could explain. So Bohr said that if we fill that an atom behaves in such a manner, we can explain all these things at once. brilliances special theory of relativity is also based on two postulates, the constancy of the speed f electromagnetic radiotherapy and the validity of phy sical laws in all inertial frame of reference. It would not be wise to ask somebody to prove that the speed of light in vacuum is constant, independent of the source or observer. In mathematics too, we need axioms and hypotheses at every stage. Euclids statement that jibe lines never meet, is a hypothesis. This means that if we assume this statement, we can explain several properties of straight lines and two or three dimensional figures made out of them. But if you dont assume it, you are free to use a different axiom and get a new geometry, as has indeed happened in he past few centuries and decades. P HYSICAL WORLD 5 theory of objects falling to the earth under gravity. 1. 3 PHYSICS, engineering science AND SOCIETY The connection between physics, technology and society can be seen in many examples. The discipline of thermodynamics arose from the need to understand and improve the working of heat engines. The steam engine, as we know, is inseparable from the Industrial Revolutio n in England in the eighteenth century, which had great impact on the course of human civilisation. Sometimes technology gives rise to new physics at other times physics generates new technology.An example of the latter is the wireless communion technology that followed the find of the basic laws of electricity and magnetism in the nineteenth century. The applications of physics are not always easy to foresee. As late as 1933, the great physicist Ernest Rutherford had dismissed the possibility of tapping energy from atoms. But only a few years later, in 1938, Hahn and Meitner discovered the phenomenon of neutron-induced fission of uranium, which would serve as the basis of nuclear power reactors and nuclear weapons. Yet other important example of physics giving rise to technology is the te chip that triggered the computer revolution in the last three decades of the twentieth century. A most significant area to which physics has and will chair is the development of choice energy resources. The fossil fuels of the planet are tapered fast and there is an urgent need to discover new and low-priced sources of energy. Considerable progress has al heary been made in this direction (for example, in conversion of solar energy, geothermal energy, etc. , into electricity), but much more is still to be accomplished. parry1. 1 lists some of the great physicists, their major contribution and the country of rigin. You will appreciate from this table the multi-cultural, international character of the scientific endeavour. card 1. 2 lists some important technologies and the principles of physics they are based on. Obviously, these tables are not exhaustive. We urge you to try to add many name and items to these tables with the help of your teachers, good books and websites on science. You will find that this exercise is very educative and also great fun. And, assuredly, it will never end. The progress of science is unstoppable Physics is the study of nature and natur al phenomena. Physicists try to discover the rules hat are operating in nature, on the basis of observations, experiment and analysis. Physics deals with certain basic rules/laws governing the natural world. What is the nature Table 1. 1 Some physicists from different countries of the world and their major contributions Name study contribution/discovery Country of Origin Archimedes regulation 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 stimulus generalization U. K. James Clerk MaxwellElectromagnetic theory Light-an electromagnetic wave U. K. Heinrich Rudolf Hertz contemporaries 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 P oland natural radioactivity Albert Einstein Explanation of photoelectric effect Theory of relativity Germany 6 P HYSICS 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 BohrQuantum 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 ionisation 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 BhabhaCascade process of cosmic radiatio n India Lev Davidovich Landau Theory of condensed matter Liquid helium Russia S. Chandrasekhar Chandrasekhar limit, structure and evolution of stars India toilet Bardeen Transistors Theory of super conductivity U. S. A. C. H. Townes Maser Laser U. S. A. Abdus Salam Unification of rachitic and electromagnetic interactions Pakistan of physical laws? We shall now discuss the nature of fundamental forces and the laws that govern the diverse phenomena of the physical world. 1. 4 FUNDAMENTAL FORCES IN NATURE* We all have an intuitive notion of force. In our experience, force is postulate to push, carry or hrow objects, deform or break them. We also experience the impact of forces on us, like when a pitiable object hits us or we are in a merry-goround. Going from this intuitive notion to the proper scientific concept of force is not a trivial matter. Early thinkers like Aristotle had wrong * ideas about it. The correct notion of force was arrived at by Isaac Newton in his famous laws of motion. He also gave an explicit form for the force for gravitative attraction between two bodies. We shall learn these matters in subsequent chapters. In the macroscopic world, besides the gravitational force, we encounter several kinds f forces muscular force, contact forces between bodies, friction (which is also a contact force parallel to the surfaces in contact), the forces exerted by compressed or extended springs and taut strings and ropes (tension), the force of buoyancy and viscous force when solids are in Sections 1. 4 and 1. 5 contain several ideas that you may not grasp fully in your first reading. However, we advise you to read them carefully to develop a feel for some basic aspects of physics. These are some of the areas which continue to occupy the physicists today. P HYSICAL WORLD 7 Table 1. 2 Link between technology and physics TechnologyScientific principle(s) Steam engine Laws of thermodynamics Nuclear reactor Controlled nuclear fission receiving set and Te levision 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 Newtons laws of motion electrical generator Faradays laws of electromagnetic induction Hydroelectric power revolution of gravitational potential energy into electrical energy Aeroplane Bernoullis principle in fluid dynamics Particle accelerators Motion of charged particles in electromagnetic ields Sonar Reflection of ultrasonic waves Optical fibres thorough internal reflection of light Non-reflecting coatings Thin film optical onus Electron microscope Wave nature of electrons Photocell Photoelectric effect coalescency 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. contact with flu ids, the force due to wedge of a fluid, the force due to surface tension of a liquid, and so on. There are also forces involving charged nd magnetic bodies. In the microscopic domain again, we have electric and magnetic forces, nuclear forces involving protons and neutrons, interatomic and intermolecular forces, etc. We shall get familiar with some of these forces in later parts of this course. A great insight of the twentieth century physics is that these different forces occurring in different contexts actually arise from only a small number of fundamental forces in nature. For example, the elastic spring force arises due to the net attraction/ horror between the neighbouring atoms of the spring when the spring is elongated/compressed. This net ttraction/repulsion can be traced to the (unbalanced) sum of electric forces between the charged constituents of the atoms. In principle, this means that the laws for derived forces (such as spring force, friction) are not independent of t he laws of fundamental forces in nature. The origin of these derived forces is, however, very complex. At the present stage of our understanding, we know of four fundamental forces in nature, which are described in brief here 8 P HYSICS Albert Einstein (1879-1955) Albert Einstein, natural in Ulm, Germany in 1879, is universally regarded as one of the greatest physicists of all time.His astonishing scientific career began with the publication of three path-breaking constitutions in 1905. In the first paper, he introduced the notion of light quanta (now called photons) and used it to explain the features of photoelectric effect that the unspotted wave theory of radiation could not account for. In the second paper, he developed a theory of Brownian motion that was confirmed experimentally a few years later and provided a convincing evidence of the atomic picture of matter. The third paper gave birth to the special theory of relativity that made Einstein a legend in his own life tim e.In the next decade, he explored the consequences of his new theory which included, among other things, the mass-energy equivalence enshrined in his famous equation E = mc2. He also created the general version of relativity (The General Theory of Relativity), which is the modern theory of gravitation. Some of Einsteins most significant later contributions are the notion of stimulated emission introduced in an alternative derivation of Plancks blackbody radiation law, static model of the universe which started modern cosmology, quantum statistics of a gas of massive bosons, and a critical analysis of the foundations of quantum mechanics.The year 2005 was declared as International Year of Physics, in comprehension of Einsteins monumental contribution to physics, in year 1905, describing revolutionist scientific ideas that have since influenced all of modern physics. 1. 4. 1 Gravitational Force The gravitational force is the force of mutual attraction between any two objects by virt ue of their masses. It is a universal force. Every object experiences this force due to every other object in the universe. All objects on the earth, for example, experience the force of gravity due to the earth. In particular, gravity governs the motion of the moon and artificial satellites around he earth, motion of the earth and planets around the sun, and, of course, the motion of bodies falling to the earth. It plays a key role in the large-scale phenomena of the universe, such as formation and evolution of stars, galaxies and galactic clusters. 1. 4. 2 Electromagnetic Force Electromagnetic force is the force between charged particles. In the simpler case when charges are at rest, the force is given by Coulombs 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 nd magnetic effects are, in general, inseparable thence the name electromagnetic force. Like the gravitational force, electromagnetic force acts over large distances and does not need any intervening medium. It is considerablely sanitary compared to gravity. The electric force between two protons, for example, 36 is 10 times the gravitational force between them, for any fixed distance. Matter, as we know, consists of main(a) charged constituents like electrons and protons. Since the electromagnetic force is so much stronger than the gravitational force, it dominates all phenomena at atomic and molecular scales. (The other two forces, as we hall see, operate only at nuclear scales. ) Thus it is mainly the electromagnetic force that governs the structure of atoms and molecules, the dynamics of chemical reactions and the mechanical, thermal and other properties of materials. It underlies the macroscopic forces like tension, friction, normal force, spring force, etc. Gravity is always attractive, while electromagnetic force can be attractive or repulsive. Another way o f set it is that mass comes only in one variety (there is no minus mass), but charge comes in two varieties positive and negative charge. This is what makes all the difference.Matter is mostly electrically neutral (net charge is zero). Thus, electric force is generally zero and gravitational force dominates terrestrial phenomena. Electric force manifests itself in atmosphere where the atoms are ionised and that leads to lightning. P HYSICAL WORLD 9 Satyendranath Bose (1894-1974) Satyendranath Bose, natural in Calcutta in 1894, is among the great Indian physicists who made a fundamental contribution to the advance of science in the twentieth century. An outstanding student throughout, Bose started his career in 1916 as a lecturer in physics in Calcutta University five years later he joined capital of Bangladesh University.Here in 1924, in a brilliant flash of insight, Bose gave a new derivation of Plancks law, treating radiation as a gas of photons and employing new statistical methods of counting of photon states. He wrote a short paper on the subject and sent it to Einstein who immediately recognised its great significance, translated it in German and forwarded it for publication. Einstein then applied the same method to a gas of molecules. The key new conceptual ingredient in Boses work was that the particles were regarded as indistinguishable, a radical departure from the assumption that underlies the classical MaxwellBoltzmann statistics.It was soon realised that the new Bose-Einstein statistics was applicable to particles with integers spins, and a new quantum statistics (Fermi-Dirac statistics) was needed for particles with half integers spins satisfying Paulis exclusion principle. Particles with integers spins are now known as bosons in honour of Bose. An important consequence of Bose-Einstein statistics is that a gas of molecules below a certain temperature will undergo a mannikin transition to a state where a large fraction of atoms survive the same lowest energy state.Some seventy years were to pass before the pioneering ideas of Bose, developed further by Einstein, were dramatically confirmed in the observation of a new state of matter in a stretch out gas of ultra cold alkali atoms the Bose-Eintein condensate. If we reflect a little, the enormous strength of the electromagnetic force compared to gravity is evident in our daily life. When we hold a book in our hand, we are balancing the gravitational force on the book due to the huge mass of the earth by the normal force provided by our hand. The latter is nothing but the net electromagnetic force between the charged constituents of our hand and he book, at the surface in contact. If electromagnetic force were not as such so much stronger than gravity, the hand of the strongest man would crumble under the lading of a feather Indeed, to be consistent, in that circumstance, we ourselves would crumble under our own weight 1. 4. 3 Strong Nuclear Force The strong nuclea r force binds protons and neutrons in a nucleus. It is evident that without some attractive force, a nucleus will be unstable due to the electric repulsion between its protons. This attractive force cannot be gravitational since force of gravity is negligible compared to the electric force.A new basic force must, therefore, be invoked. The strong nuclear force is the strongest of all fundamental forces, about 100 times the electromagnetic force in strength. It is charge-independent and acts equally between a proton and a proton, a neutron and a neutron, and a proton and a neutron. Its range is, however, extremely small, 15 of about nuclear dimensions (10 m). It is responsible for the stability of nuclei. The electron, it must be noted, does not experience this force. Recent developments have, however, indicated that protons and neutrons are built out of still more elementary constituents called quarks. . 4. 4 Weak Nuclear Force The clear nuclear force appears only in certain nuclea r processes such as the ? -decay of a nucleus. In ? -decay, the nucleus emits an electron and an uncharged particle called neutrino. The weak nuclear force is not as weak as the gravitational force, but much weaker than the strong nuclear and electromagnetic forces. The range of weak nuclear force is exceedingly small, of the order of 10-16 m. 1. 4. 5 Towards Unification of Forces We remarked in section 1. 1 that unification is a basic quest in physics. Great advances in physics often amount to unification of different 10 P HYSICS Table 1. Fundamental forces of nature Name Relative strength Range Operates among Gravitational force 10 39 unfathomable All objects in the universe Weak nuclear force 1013 Very short, Sub-nuclear surface ( ? 16 m) 10 Some elementary particles, particularly electron and neutrino Electromagnetic force 102 immeasurable Charged particles Strong nuclear force 1 Short, nuclear size ( ? 15 m) 10 Nucleons, heavier elementary particles theories and domains. New ton unified terrestrial and celestial domains under a common law of gravitation. The experimental discoveries of Oersted and Faraday showed that electric and magnetic phenomena are in general nseparable. Maxwell unified electromagnetism and optics with the discovery that light is an electromagnetic wave. Einstein attempted to unify gravity and electromagnetism but could not succeed in this venture. But this did not deter physicists from zealously pursuing the goal of unification of forces. Recent decades have seen much progress on this front. The electromagnetic and the weak nuclear force have now been unified and are seen as aspects of a single electro-weak force. What this unification actually means cannot be explained here. Attempts have been (and are being) made to unify the electro-weak and the trong force and even to unify the gravitational force with the rest of the fundamental forces. Many of these ideas are still speculative and inconclusive. Table 1. 4 summarises some of t he milestones in the progress towards unification of forces in nature. 1. 5 NATURE OF PHYSICAL LAWS Physicists explore the universe. Their investigations, based on scientific processes, range from particles that are small than atoms in size to stars that are very far away. In addition to finding the facts by observation and experimentation, physicists attempt to discover the laws that summarise (often as mathematical quations) these facts. In any physical phenomenon governed by different forces, several quantities may change with time. A remarkable fact is that some special physical quantities, however, remain constant in time. They are the conserved quantities of nature. soul these conservation principles is very important to describe the observed phenomena quantitatively. For motion under an external conservative force, the total mechanical energy i. e. the sum of kinetic and potential energy of a body is a constant. The familiar example is the free fall of an object under gravi ty. Both the kinetic energy