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PHYSICAL WORLD, , EEE, , 1.1 Introduction, 1.2 Physics — Scope and, Excitement, 1.3 Physics, Technology and, Society, 1.4 Fundamental Forces in, Nature, 1.5 Nature of Physical Laws, ¢ Summary, © Exercises, , 1.1 Introduction, , Dear students, welcome to you all to this first lecture, on Physics. Till Std. X, you have gained priliminary ideas, about optics, electricity, magnetism, motion, force,, gravitation, heat, energy, wave, sound, universe, etc. under, the subject science. These topics are related to physics., , Now, you may raise a question : What is Physics ?, Dear students, physics is one of the basic disciplines in, the category of natural sciences. Physics is a science to, understand nature. The word ‘Bhautik Vigyan’ (used in, Hindi / Gujarati) related to the science of physical world, is derived from Sanskrit word ‘Bhautiki’. Science of, studying the basic laws of nature and their manifestation, in different natural phenomena is Physics. Man has always, been curious about the world around him. Because of this, curiosity, man has observed the physical environment, carefully, searched meaningful patterns and relations in, natural phenomena; and still continues to do so. Conclusions,, facts, theories etc. derived from all these attempts means, physics. The english word ‘physics’ comes from a Greek, word meaning ‘nature’., , Use of mathematics is very wide spread in physics., Mathematical theories, formulae or mathematical models, are inseparable from physics. As a famous quotation, states “physics is the king of science while mathematics, is the queen.” The Mathematical expressions obtained, for some physical event, not only provide logical, explanation of that event but also make predictions, about many other connected events. Our physical facilities,, ever since existence of humans to till date, are also due, to physics.

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1.2 Physics - Scope and Excitement, , Dear students, a teacher speaks in the, classroom and you hear it. Have you analyse, this event, any time ?, , How is sound produced, when a teacher, speaks ?, , How this sound propagates in the, classroom ?, , How do your ears receive this propagated, sound ?, , Similarly, have you thought about the annual, cycle of seasons, the eclipse, the tides, the, regular repetitions of day and night, the bright, celestial objects in the night sky, etc. ?, , In physics (i) we not only observe such, physical events, taking place in our day to, day life, but find out definite mechanisms, from the series of systematic observations., , (ii) The quantities involved in such, events are to be defined unambiguously, and meanigfully,, , (iii) To derive laws or principles from, such studies, and, , (iv) Such derived laws or principles are, to be tested in wide perspectives., , Physics involves study of two fundamental, constituents of the universe : matter and, radiation, to find out origin of fundamental, particles of matter and radiation, the, interaction between them, the laws of nature, related to them, etc., , If we think further about matter, then, comes the nucleus of the atom. Here interaction, among neutrons, protons, mesons etc.; the, energies of the nucleus with radius of the order, 10m, formed due to such interactions; the, radiation emitted due to intra nuclear transitions,, etc. are the subject matter of nuclear physics., , Electrons revolving around the nucleus in, specific orbits of orbit radius 107m with, specific numbers and electronic configurations,, their transitions, their interactions, special, properties of atom because of electrons, etc., are all included in physics., , Due to interaction among atoms, molecules, are formed. These atoms do not remain, stationary inside a molecule, but perform, rotational and vibrational motions. By studying, , the radiations emitted from atoms and, molecules, we can get insights into their, structure. From such physics, various aspects, of chemistry are also understood., , When many molecules and atoms combine, together, we get different phases of matter, namely gas, liquid and solid; depending on, physical conditions. Under certain temperature, and other conditions, we also get the fourth, state of matter - plasma. The plasma state, of matter obtained at extreme high, temperature opened up a possiblity as a, future source of tremendous energy for use, of mankind., , The mechanical, thermal, electrical,, magnetic and optical properties of matter are, studied in physics. Dear students, now you, will realies that to know and understand all, such properties of different subdisciplines of, physics like mechanics, thermodynamics,, electromagnetics, optics, electrodynamics have, been developed., , Mechanics is based on Newton’s laws of, motion and law of gravitation. It is concerned, with the motion of particles, rigid and, deformable bodies, force, work, etc., Electrodynamics deals with electric and, magnetic phenomena associated with charged, and magnetic bodies. Here, how we forget, the contribution of physicists like Coulomb,, Oersted, Ampere, Faraday, Maxwell !!!, , The working of optical fibre, telescopes, and microscopes; colours exhibited by thin, films, rainbow, mirage; images formed by the, mirrors and lenses, etc. are explained in optics., , Thermodynamics includes changes in, internal energy, temperature, entropy, etc., of, the system through external work and transfer, of heat. The efficiency of heat engines and, refrigerators, the direction of physical and, chemical process, etc., are also studied in, thermodynamics., , In physics we discuss a space having, infinite dimensions. The operators in quantum, mechanics in such a space and their, operations on vectors are also very exciting., , But this is not the end of physics at all., Studies related to sun and its planetary system

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PHYSICAL WORLD, , , , is also carried out in physics. Galaxies, and, their structure, the large distance of the order, of billion light years amongst them, distribution, of billions of kilograms of their matter, the, intergalactic space; birth, evolution and death, of various stars etc. are also studied in, astrophysics, a branch of physics., , Dear students, thus we have seen that, the span of physics is from almost, ‘vacuum’ to ‘infinity’. Even, vacuum is, also considered as some definite state in, physics., , Thus the scope of physics on the length, scale is from very small length of 10-'4m, , (radius of nucleus) to 107m (length of, galaxies). Thus the factor of length scales, is of the order of 10°., , The range of the time scale, about 10-? s, to 10!®s, can be obtained by dividing the, length scales by the speed of light., , The range of mass varies from 107° kg, , (mass of an electron) to 10° kg (mass of, known observable universe)., , Table 1.1 to Table 1.3 show the range of, these fundamental physical quantities of, length, time and mass., , Table 1.1 : Order of the length scale for different objects (only for information), , , , , , , , , , , , , , , , , , , , , , , , , , Size or Distance of object Order of length scale (m), Radius of a proton 105, Radius of atomic nucleus 10-4, Size of the hydrogen atom 19°?, Thickness of a paper 10%, Height of a human 10°, Height of the Mount Everest above sea level 10*, Radius of the Earth 107, Distance of the Sun from the Earth 10, Size of our galaxy 107!, Distance to the boundary of observable Universe 10”, , , , , , , , Table 1.2 : Order of the time interval, for various events (only for information), , Table 1.3 : Order of the mass-scale for, different objects (only for information), , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , Order of Order of, Event Time Object Mass-scale (kg), interval 5) Electron 10, Life span of most unstable particle 10% Proton 1077, Time required for light to, cross a nuclear distance 10-7 Dust particle 10°, Period of atomic vibrations 10° Mosquito 103, Period of a sound wave 10° 5, Wink of eye 107 Gmpe 10°, Time between successive 3 Human 107, human heart beats 10 Earth 1, Rotation period of the Earth 10°, Revolution period of the Barth 10° om 10°, Average human life span 10° Milkyway galaxy 10", Age of the Universe 10” Observable Universe 10%

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PHYSICS, , , , The scope of physics extends over two basic, and interesting domains : macroscopic to, microscopic. In addition, it covers static and, dynamic systems. Thus physics is associated with, time, matter and energy., , Dear students, normal events like an object, falling on the earth under freefall and flight of a, balloon filled with light gas from earth; sinking of, a pin or needle in water while floating of a ship, on water; or the most advanced projects like, , Large Hadron Collider (LHC), International, Thermonuclear Experimental Reactor (ITER) and, moon mission attract us toward the study of, physics., , You may be familiar with the names of, internationally famous Indian physicists : C. V., Raman, J. C. Bose, M. N. Saha, Homi Bhabha,, S. N. Bose, Vikram Sarabhai, S. Chandrashekhar,, etc. List of some Indian institutes doing research, in the field of physics is given in Table 1.4 for, your information, only., , Table 1.4 : List of some of the Indian Institutes doing Research in the Field of Physics, (only for information), , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , Name of the Institutes Place, Bhabha Atomic Research Centre (BARC) Mumbai, Physical Research Laboratory (PRL) Ahmedabad, Institute for Plasma Research (IPR) Gandhinagar, Institute of Physics (IOP) Bhuwaneshwar, National Physical Laboratory (NPL) Delhi, Inter University Consortium for Astronomy and, Astrophysics (IUCAA) Pune, Indian Institute of Science (IISc) Bangalore, Raman Research Institute (RRI) Bangalore, Tata Institute of Fundamental Research (TIFR) Mumbai, Centre for Advance Technology (CAT) Indore, Nuclear Science Centre (NSC) Delhi, Indira Gandhi Centre for Atomic Research (IGCAR) Kalpakamm, Saha Institute of Nuclear Physics (SINP) Kolkatta, Regional Research Laboratory (RRL) Bhopal, Inter University Acelerator Centre (UAC) Delhi, Veriable Energy Cyclotron Centre (VECC) Kolkatta, Vikram Sharabhai Space Centre (VSSC) Banglore, Indian Institute of Astrophysics (ILA) Banglore, Indian Institute of Geomagnetism (IIG) Mumbai, Indian Space Research Organization (ISRO) Various places in India, Space Applications Centre (SAC) Various places in India, Indian Institute of Technology (IIT) Various places in India, National Institute of Technology (NIT) Various places in India, Various Universities Various places in India

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13 Physics, Technology and Society, , Today, we can reach any corner of the, world within few hours, we can talk to a, person sitting at any corner of the world within, few seconds. While sitting at the home, we, can see live telecast of an event or a game, taking place at other places in the world. We, can take photographs of our solar system and, galaxies. All these become possible because of, physics., , The progress made in transportation, vehicles : bullock cart, bicycle, motor cycle, car,, ship, aeroplane; telegram, telephone, mobile,, satellite phone used in communication; radio, tape, recorder, television used in entertainment and, heaters keroseene stove, gas stove, microwave, oven etc. used in kitchen, have become possible, because of the proper use of laws or theories of, physics in technology., , It is physics which introduced us to radiations, and taught us to accelerate charge particles,, physics gave instruments based on ultrasonic and, optical fibres. Very useful medical technology like, X-rays, sonography, Electro Cardio Graf (ECG),, Electron Spin Resonance (ESR), Nuclear, Magnetic Resonance (NMR), Endoscopy are also, due to physics., , Instruments like microscope, Electron, Microscope (EM), Atomic Force Microscope, (AFM) have played a vital role in the development, of material technology, nenotechnology and, biotechnology., , You would possibly not be unaware of space, technology. Rocket, missile, space shuttle, manmade satellite, remote sensing, etc. also, are, words in common use. You may have heard about, lasers, radar and microwaves., , Physics has taught us the technique of, achieving very low temperatures which results in, the development of cryogenics. Physics is the, mother of subjects like electronics and, communication, computer technology, and, information technology., , Even after this tremendous development we, are still not in a position to say that we have, fully understood nature. Many problems are still, unresolved for physicists. For example does, universe consist of a single element ? Are matter, , and energy two different aspects of the same, thing ? Is unification of various forces in nature, possible ? What is the future of universe ?, , Forced with severals questions like these,, Physicist are attempting to solve two principal, thrusts in physics : unification and reduction., 14 Fundamental Forces in Nature, , Dear students, if we want to roll a ball on, the ground (surface) then we have to apply force, to give motion to the ball. The ball will stop, after travelling a certain distance since, frictional force is acting on the surface of the, ball. We have to use a force to lift a ball from, the surface. We also feel force when someone, pulls or pushes us. Thus, we experience forces, in day-to-day life in various ways. Starting from, such rudimentary concept of force we will lean, the scientific concept of force., , Isaac Newton was the first physicist who, developed clear concept of force in his famous, laws of motion. In addition, he also discovered, the universal law of gravitation., , Inthe macroscopic domain, besides, gravitational force, we come across many different, types of forces such as frictional force between, two surfaces, the restoring force arising in a, compressed spring, tension produced in a stretched, string the force of surface tension prevailing in, the free surface of a liquid, the viscous force in, a fluid medium, etc., , In addition to these, force is also generated, because of electrically charged and magnetic, objects. Electric and magnetic forces, nuclear, forces, interatomic and intermolecular forces, etc., are the examples of the forces prevailing in the, microscopic domain., , At present, it is understood that there exist, only four fundamental forces in nature. Let us, understand them qualitatively., , 1.4.1 Gravitational Force, , The gravitational force is a universal force, and every object experiences this force due to, every other object in the universe. According to, Newton’s law of gravitation, thc mutual, attractive force is directly proportional to the, product of their masses and inversely, proportional to the square of the distance