Tiêu đề PHYSICS CRASH COURSE.pdf ✅

1.1 What is Physics? Physics is derived from the Greek word fusis, it means : nature. Therefore, physics is the science in which we go through the scientific studies of nature and natural incidents. What is nature? Whatever be in the universe, that is all nature. Fauna, flora, buildings, the earth, the sky, water, air etc all are made of matter and energy. Matter: Such each particle or object, having the mass, which occupy the space and to whom we can experience directly or indirectly with our sense organs, is called matter. Example: Water, air, stone, iron, wood, mol e cule, elec tron etc. Energy: The ability of an object to do work is called energy. There are many forms of energy in the universe, such as ; mechanical energy, electrical energy, magnetic energy, nuclear energy, heat, light, sound etc. Various forms of energy can be converted to each other. Work can also be converted into energy. Previously it was believed that matter and energy do not have any mutual relation but in the starting of 20 th century great scientist Einstein propounded that matter and energy are the two sides of the same coin. These can be converted to each other according to following relation: E = mc 2 Where E is the equivalent energy for the matter of mass m. Here c is the speed of light in vacuum. Therefore, the latest definition of physics is provided as follows : ‘‘Physics is the science in which we go through matter, energy and their mutual actions, secrets are mentioned as of natural incidents by micro and macro matters.’’ Remember that chemical reactions of matter and energy are not the content of physics. 1.2 Scope and Excitement of Physics Fundamentally physics is divided into two parts : (A) Macroscopic Under the macro impact region, phenomenon of laboratory, terrestrial and astronomical level occur. Explanation of these phenomenon is based on the principles of classical physics. Following sub-topics of physics are included in it. (i) Me chan ics: Un der it, we study the mo tion of par ti cles, rigid and dis torted bod ies and sys tems of the par ti cles at equi lib rium state and mov ing with less speed. This is the sub ject based on the New ton’s laws of mo tion and grav i ta tional laws. The pos tu late of phys i cal quan ti ties such as; force, mass, ac cel er a tion, in er tia, lin ear mo men tum, work , en ergy and power etc are rep re sented in it. (ii) Thermodynamics: Un der it (In com par i son to me chan ics) we do not con sider the over all speed of ob jects but con sider the sys tem in mac ro scopic bal ance. In it we study about tem per a ture, heat, work a heat con ver sion, in ter nal energy etc. (iii) Oscillations and Wave: Un der it we study about vi bra tions of the ob jects, gen er ated tur bu lence from vi bra tions and its trans mis sion and sound etc. (iv) Optics: Un der it we study the phenomenon based on light. (v) Electrodynamics: Under it we study about the electric and magnetic phenomenon related to charged and magnetic objects. Its fundamental laws are known as four equations of Maxwell. (B) Microscopic Under the micro impact region, atomic, molecular and nuclear phenomenon occur. In these phenomenon we study about mutual actions with composition, structure of matter and its various fundamental particles (e. g., electron, proton, neutron etc.) on the scale of atomic distances (≈ ) − 10 10 m and nuclear Physical World 1 Physical World CHAPTER 1
distances (≈ ) − 10 14 m . These phenomenon can not be explained by the principles of classical physics. These micro phenomenon are explained on the basis of quantum principle of modern physics. Fol low ing are the sa lient sub-top ics of phys ics in cluded in mod ern phys ics. (i) Atomic Physics: Un der it we study about the phe nom e non which hap pen out of the nu cleus in atom. (ii) Nuclear Physics : Un der it we study about the phe nom e non hap pen ing in side the nu cleus in atom. Study of physics is provoking and interesting. Here we study about even very micro elements such as ; electron, proton, etc upto giant celestial bodies such as ; planet, the sun, galaxy etc. In this study vast premises of length and mass are used. For example, for study of phenomenon related to electron and proton, very micro scale (≈ ) − 10 14 m of length is used. This fact can be very interesting for a person that phenomenon may explain the vast premises of physical quantities of physics by laws and basic concepts of physics. On one side we study the nuclear events on very small scale (≈ ) − 10 14 m , while on the other side we study about astronomical events on very large scale (≈ 10 ) 26 m of length. While a side we study a particle of very small mass (≈ ) − 10 30 kg , i. e., electron, on the other side we study the known world of very large mass (≈ 10 ) 55 kg . How it is interesting that by which law the motion of electron around the nucleus is explained, orbital motion of the earth around the sun is also explained by the same law. We came to know about the new laws of physics by obtained observations and experiments done in our daily life. On the basis of it we get some important discoveries from physics. Newton propounded the law of gravitation by seeing a falling apple. On seeing the incident of up and down motion of a lid of a kettle due to exerting steam, James Watt propounded the principle of steam engine. On seeing the deflection of galvanometer connected with coil on throwing magnet inside the coil, Faraday propounded the law of electromagnetic induction. On seeing the sudden zerk in the body of a frog when we take tweezers, made of two different metals, in the liquid of frog’s body, Gelvani led the way for construction of Volta cell. At present so many interesting and beneficial exploration for human beings are taking place. 1.3 Fundamental Forces in Nature Various phenomenon occurring in nature are controlled by the forces. These phenomenon can be understood in terms of the following four fundamental forces, which govern the macroscopic as well as microscopic world : 1. Gravitational forces 2. Weak nuclear forces 3. Electromagnetic forces 4. Strong nuclear forces. 1. Gravitational Forces : The grav i ta tional force is the force of at trac tion which acts be tween the two bod ies by vir tue of their masses. 2. Weak Nuclear Forces : The weak nu clear forces are the forces of in ter ac tion act ing be tween el e men tary par ti cles of short life times which are de vel oped in some nu clear re ac tions. For ex am ple : These forces act between : (i) leptons and leptons (ii) leptons and mesons 3. Electromagnetic Forces : These forces act be tween two sta tion ary or mov ing charges. 4. Strong Nuclear Forces : The forces which are re spon si ble for bind ing neu trons and pro tons to gether in side the nu cleus are known as strong nu clear forces. äRemark The relative strengths of four basic forces in nature can be written as: FGravitational FWeak FEm FStrong : : : = 1 10 10 10 25 36 38 : : : S.No. Name Rel a tive strength Range 1. Gravitational force 1 Infinite 2. Weak nuclear force 10 25 ≈ − 10 16 m 3. Electromagnetic force 10 36 Infinite 4. Strong nuclear force 10 38 ≈ − 10 15 m (nuclear size) 1.4 Unification of Forces A lot of work has been done towards the unification of various theories and domains of physics. Some of them are listed below: (i) Oersted and Faraday showed that elec tric and mag netic phe nom e non can not be sep a rated. Oers ted es tab lished that a cur rent car ry ing con duc tor pro duces mag netic field in its sur round ing re gion, i. e., mag ne tism can be pro duced with the help of elec tric ity. Far a day showed that in duced emf and cur rent can be produced by using magnetism. (ii) Maxwell uni fied op tics, elec tric ity and mag ne tism and it was es tab lished that light is an elec tro mag netic wave. (iv) Newton unified terrestrial and celestial mechanics confirming that same laws of motion and the laws of gravitation are applicable to both. 2 Crash Course Physics for NEET
Name of the 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 1820 Showed that electric and magnetic phenomena are Michael Faraday 1830 inseparable aspects of a unified domain; electromagnetism. James Clerk Maxwell 1873 Unified electricity, magnetism and optics; showed that light is an electromagnetic wave. Sheldon Glashow, Abdus Salam, Steven Weinberg Showed that the ‘weak’ nuclear force and the electromagnetic force could be viewed as different aspects of a single electro-weak force. Carlo Rubia, Simon Vander Meer 1984 Verified experimentally the predictions of the theory of electro weak force. 1.5 Nature of Laws of Physics Fundamental laws of physics are universal, i. e., these can be applicable in various contents. Majority of the laws can be expressed by obvious mathematical equations. These equations represent the relation between two or more physical quantities. Physicist study the natural phenomenon by experiments and observations and try to discover the new laws. In daily life most of the natural phenomenon are highly complexed. On the basis of obtained observations complexity of a phenomenon cannot be clear in one go. For this, first of all fundamental principles are discovered on the basis of critical characteristic of natural phenomenon. Then these principles are made more accurate by interleaving the purification. For example: when Galileo studied about the bodies falling freely under gravity then presence of air resistance made the observations highly complicated. Therefore, to establish fundamental law of free fall under gravitational force, Galileo completed his experiment in such conditions in which air resistance was negligible. This law could be established from the obtained observations that the rate of velocity change of the body with respect to time in free fall remains constant but it does not remain constant with distance. Due to air resistance other important conclusions are obtained by interleaving the purification in bar of the nature. Various physical quantities in a physical phenomenon change with time but the value of some specific quantities remains constant with time. Such quantities are called conserved quantities and the law, of (being conserved) these quantities, are called law of conservation. Some salient conservation laws are as follows: 1. Law of Conservation of Mechanical Energy: Mechanical energy (Kinetic energy + Potential energy) of a body remains constant during motion under conservative forces. 2. Law of Con ser va tion of En ergy : To tal en ergy (along with mass) of an iso lated sys tem re mains con served. 3. Law of Con ser va tion of Lin ear Mo men tum : If no ex ter nal force is act ing on a sys tem then its lin ear mo men tum re mains conserved. 4. Law of Conservation of Charge: Net charge of an iso lated sys tem re mains con served. Fundamental rules of physics do not change with time and place. Therefore, property of conservation is found in them. 1.6 Applications of Physics in Technology and Society In industry, apparatus, instruments and devices of various types are manufactured by using the laws and principles of physics by which production has increased and changes in social conditions, relations, arrangement and structure have come. Followings are some example of it; (i) Projection of artificial satellite and space crafts is possible from universal gravitation. Stationary satellite is used in telecommunications for prediction of weather. (ii) By the study of principles of thermodynamics, heat engine and refrigerator are developed. (iii) Hydro power and nuclear power generating stations can be established by the principle of energy conservation devices such as : motor and generator are made of this principle. (iv) Various optical instruments like microscope, telescope, cinema projector, camera etc could be manufacture by the principle of optics. (v) We can detect the broken bone in any part of the body with the help of X-rays, the creation of modern physics. (vi) So many isotopes are discovered after invention of radioactivity and they are used in prognosis, agriculture and other commercial regions. (vii) Computer is manufactured by the principles of electronics which is used in every region of today’s life. Sometimes physics raises new technology, some times new technology raises physics. Communication technology Physical World 3