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Chapter 1, , Physical World, , © Introduction Introduction, , © What is Physics? “What has all of this to do with my life? Why should I study, Physics?” If you think on these lines, the reply is, "Physics has got, , © Some and Retement yf enough to do with the real life. Do you want to be the first person, , Physics to invent a spaceship which travels faster than light or a car that, © Physics, Technology and runs on water...? All of you have the potential and realizing this, Society starts right here, right now. You can reason from basic physics, , concepts all the way to valid conclusions about the world around, e Fundamental Forces in Nature you and the fun is in this understanding. Physics is the foundation, of all engineering and technology. Could any engineer design a, spaceship, a LED TV or a mobile phone which all of you use without, e Some Important Definitions first understanding the basic laws of physics. When we look around, us at this fascinating, magnificent and immense cosmos - look at, the awesome, vast cosmos - planets moving around the sun in an, © Quick Recap orderly manner, phases of moon or movement of machinery parts all of them are following certain laws. The inquiring and imaginative, human mind responds to this in many ways. One such response is, to observe carefully, look for meaningful patterns, predict events,, control environment. Don't you want to be the incharge of your, environment with this powerful tool - Physics? This study is also an, adventure. You will find it challenging, richly rewarding and, satisfying. It will appeal to your sense, of beauty. Lets take a step, forward by understanding ‘Physical World’. In this chapter, you, will study what is physics; its scope and excitement; physics,, technology and society; fundamental forces in nature and nature of, physical laws., , © Nature of Physical Laws, , © Formulae Chart, , WHAT IS PHYSICS?, , Origin of the word, ‘Science’, is from Latin word, ‘Scientia’ which means, ‘to, know’. The Sanskrit word, ‘Vigyan' also has similar meaning, i.e., knowledge., The early civilisations also made important contribution to its progress., , Aakash Educational Services Pvt. Ltd. Regd. Office : Aakash Tower, 8, Pusa Road, New Dethi-110005, Ph. 011-47623456

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2 ~~ ~Physical World Board & Competitive Exams., , , , Science is a systematic (step by step) knowledge acquired through observation and experience, aimed at, understanding natural phenomena in as much detail as possible. This knowledge is used to predict and control, our environment., , The first step towards the discovery of science is a child's curiosity to learn about the world and disclose, the secrets of nature. Let this child in you be alive., , Scientific method involves, , 1., 2., , ‘Systematic observation : It is setting up our study so that we eliminate or reduce bias., , Controlled experiment : It generally compares the results obtained from an experimental sample, against a control sample, which is practically identical to experimental sample except for the one aspect, whose effect is being tested (the independent variable), e.g., you want to know whether light or dark, clothing would be more comfortable on a hot, sunny day. A controlled experiment involves setting up, two experimental conditions that are exactly same except for a single factor that the scientist, manipulates. Here, the factor is colour. You will apply a heat source, represented by a 60 W light bulb, to different coloured jackets and compare the temperature change for each other., , Qualitative and quantitative reasoning : Qualitative measurement is at the heart of growth of science, as laws of nature expressible in precise mathematical equations., , Mathematical modelling : It is the process of developing a mathematical model (Description of a, system using mathematical concepts and language), e.g., predicting the position of a vehicle from its, initial position, direction and speed of travel, using the equation that distance travelled is the product of, speed (constant) and time. It is common to use idealized models in physics to simplify things. Massless, ropes, point particles, ideal gases are among the many simplified models used in Physics. The laws, of physics are represented by simple equations such as Newton's laws, Maxwell's equations. Many real, life situations are very complex and thus modeled approximate., , Prediction : It is a scientific statement about a future event. It is based on a scientific theory. It means, in particular it is reproducible, consistent and the theory it is based on, is not in conflict with already, available data. It is scientifically falsifiable., , Verification or falsification of theories : Falsifiability or reputability of an assertion, hypothesis or, a theory is the logical possibility that it can be contradicted by an observation or the outcome of a, physical experiment that something is ‘falsifiable’ does not mean it is false, rather if then some observation, or experiment will produce a reproducible result, that is in conflict with it, e.g., the assertion that ‘all swans, are white’ is falsifiable because it is logically possible that a swan can be found which is not white. If, one finds one single black swan, logic admits the conclusion that the statement that all swans are white, is false. Falsification thus strives for questioning for falsification of hypothesis, instead of proving them., The statement ‘all swans are white’ is falsifiable because it can come in conflict with the observation, that ‘this swan is black’. In contrast, the statement that ‘white swans do exist’ is not falsifiable as no, counter example is logically possible., , , , Not everything can be proved in physics and mathematics, e.g., the universal law of gravitation is, an assumption or a hypothesis. Newton explained several observations, experiments and data of, the planetary motion, bodies falling towards earth by making an assumption that any two bodies, 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. With this, he was able to explain, all the observations. Not only that, it allows us to predict the results of future experiments., A hypothesis is a supposition without assuming that it is true., , , , , , Aakash Educational Services Pvt. Ltd. Regd. Office : Aakash Tower, 8, Pusa Road, New Delhi-110005, Ph. 011-47623456

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Board & Competitive Exams. Physical World 3, , , , A model is a theory proposed to explain observed phenomena, e.g., in Bohr’s model of hydrogen, atom, it is assumed that an electron in the hydrogen atom follows certain rules (postulates). Bohr, , was able to explain a large amount of spectroscopic data with the assumption that an atom behaves, in such a manner., , Theory : In physics, this term is generally used for a mathematical framework - derived from a small, set of basic postulates (usually symmetries - like equality of location in space or in time, or identity, of electrons etc.) which is capable of producing experimental predictions for a given category of, Physical systems. Einstein's special theory of relativity is based on two postulates, the constancy, of the speed of electromagnetic radiation and the validity of physical laws in all inertial frames of, reference. You cannot ask somebody to prove that the speed of light in vacuum is constant,, independent of the observer., , An axiom is a truth which is self-evident. An axiom or a postulate is a preposition that is not and, cannot be proven within the system based on them. It is a logical statement that is assumed to, be true. Its truth is taken for granted within the particular domain of analysis, and serves as a, starting point for deducting and inferring other (theory and domain dependent) truths., , , , , , , , , , Knowledge Cloud |, , Basic steps that scientists follow :, , n, i C Construct hypothesis >»———_C Think and Try again »), , , , , , , , L Ask a question : Scientific method starts with asking a question about something that you observe:, How, What, When, Who, Which, Why or Where? In order for scientific method to answer the question,, it must be about something that you can measure, preferably with a number., , ll. Do background research : Use library and internet research to help you find best ways to do things, and ensure that you do not repeat mistakes from the past., , il. Construct a hypothesis : A hypothesis is a supposition without assuming that it is true. It is an, educated guess about how things work., , "If (1 do this) , then _(this) _ will happen.”, , Aakash Educational Services Pvt. Ltd. Regd. Office : Aakash Tower, 8, Pusa Road, New Deihi-110005, Ph. 011-47623456

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4, , Physical World Board & Competitive Exams., , , , , , You must state your hypothesis in such a way that you can easily measure and of course your, hypothesis should be constructed in a way to help you answer your original question., , IV. Test your hypothesis by doing an experiment : It is important for your experiment to be a ‘fair test’., A ‘fair test’ occurs when you change only one factor (variable) and keep all other conditions the same., You should also repeat your experiment several times to make sure that the previous results were not, just an accident., , Vv. Analyze your data and draw a conclusion : Collect your measurements and analyze them to see, if your hypothesis is true or false. Scientists often find that their hypothesis was false and in such cases,, they will construct a new hypothesis starting entire process of scientific method once again. Even if their, hypothesis was true, they may want to test it again in a new way., , Vi. Communicate your result : Scientists publish their final result in a scientific journal or by presenting, their results on a poster at a scientific meeting., , , , , , Science cannot be static. We cannot have a ‘final theory’. A theory has to account for new experimental, results and required, by modifying it. When existing theory is unable to do it, it leads to a new theory, e.g.,, entirely new theory (quantum mechanics) was developed for atomic and molecular phenomena when Newtonian, mechanics could not explain some of its basic features., , A scientist may introduce a concept theoretically like Paul Dirac (1902-1984) introduced the concept of, antiparticle theoretically in 1930, which was confirmed in 1932 by experimental discovery of positron, (antielectron) by Carl Anderson., , ‘Physics’ is one of the many, disciplines of Science. Its origin is from a Greek word ‘Fusis’, which means, ‘nature’. Its Sanskrit equivalent is ‘Bhautiki’. Physics is the branch of science, devoted to the study of nature, and natural phenomena. It deals with the study of inanimate matter, energy and radiation., , Two main thrusts in Physics are : (i) Unification and (ii) Reduction., , 1. Unification is explaining diverse physical phenomena in terms of a few concepts and laws, e.g., the, same law of gravitation given by Newton explains planetary motion, motion of moons around a planet, and a body falling to the ground., , 2. Reduction is deriving the properties of a bigger, more complex system from the properties and interaction, of its constituent simpler parts, e.g., in thermodynamics, the temperature is related to the average kinetic, energy of molecules of the system., , Example 1: What are the interconnected steps of the scientific method?, , Solution : (a) Systematic observations, , (b) Controlled experiments, , (c) Qualitative and quantitative reasoning, (d) Mathematical modelling, , (e) Prediction, , (f) Verification or falsification of theories, , , , Example 2: What is Physics?, Solution : It is a branch of science devoted to the study of nature and natural phenomena. It deals with the, , study of inanimate matter, energy and radiation., , , , Aakash Educational Services Pvt. Ltd. Regd. Office : Aakash Tower, 8, Pusa Road, New Deihi-110005, Ph. 011-47623456

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Board & Competitive Exams. Physical World 5, , , , 1. | What are the suggested basic steps that scientists follow?, , [Hint : Question, research, hypothesis, experiment, conclusion. Is it true? Report result], 2. Can everything be proved in Physics?, , [Hint : Universal law of gravitation], 3. What is falsifiability?, , [Hint : Think about the assertion. All swans are white. Being contradicted by......], , , , , , SCOPE AND EXCITEMENT OF PHYSICS, The two domains in Physics are : Macroscopic and Microscopic., , , , Macroscopic Domain, , The macroscopic domain includes the study of phenomena involving objects of finite size at the laboratory,, terrestrial scale and even on astronomical scale. This is classical physics. It includes mechanics,, electrodynamics, optics and thermodynamics., , Mechanics deals with the study of general system of particles, rigid and deformable bodies, rocket propulsion,, Propagation of water waves or sound waves etc., , Electrodynamics deals with charged and magnetic bodies and electric and magnetic phenomena associated, with them. Coulomb, Oersted, Ampere and Faraday gave its basic laws which were encapsulated by Maxwell, in his beautiful set of equations. Some key problems are motion of a current carrying conductor in a magnetic, field, propagation of radio waves and generation of electric power., , Optics deals with the phenomena associated with light, i.e., reflection, refraction, interference, diffraction,, polarisation and optical instruments like microscopes, telescopes., , Thermodynamics deals with systems in macroscopic equilibrium and related with changes in temperature,, entropy etc. The efficiency of heat engines and refrigerators etc. are the problems of interest., , Microscopic Domain, , The microscopic domain includes atomic, molecular and nuclear phenomena. It deals with the constitution, and structure of matter at atomic and nuclear scale (and even lower scales of length) and their interaction, with the elementary particles like electrons, protons. Classical physics could not handle this domain, so we, now have quantum theory as the proper framework for microscopic world. Overall, you will appreciate the beauty, of Physics more as you pursue it., , You will appreciate the vastness of scope of Physics. At one end, we have phenomena at very small scale, of length (10-4 m or even less) involving elementary particles; at the other end, we have astronomical, phenomena (of the order of 1078 m). The two scales differ by a factor of 10*° or even more. The range of time, , 14, , , , 1, scale is obtained by dividing the length scale by the speed of light, he. 98, , The range of mass is from 10-*' kg (mass of an electron) to 10% kg (mass of known universe). The terrestrial, phenomena is in the middle of this range., , 1076, = 10-22 —— = 10%, 1 sto 10° 10% s., , Aakash Educational Services Pvt. Ltd. Regd. Office : Aakash Tower, 8, Pusa Road, New Deihi-110005, Ph. 011-47623456