physical world class 11 physics chapter 1 notes || What is physics Class 11 || WHAT IS SCOPE AND EXCITEMENT OF PHYSICS || Hypothesis axioms and models || HOW PHYSICS TECHNOLOGY AND SOCIETY ARE CO-RELATED?

 Topics to be mentioned

* what is Physics?

* Scope and excitement of physics

* Physics, technology and society

physical world class 11 physics chapter 1 notes 

What IS PHYSICS Class 11


Physics is the branch of science that deals with the structure of matter and how the fundamental constituents of the universe interact. It studies objects ranging from the very small using quantum mechanics to the entire universe using general relativity.


People have continuously been inquisitive almost the world around them. The night sky with its shinning ethereal objects has captivated people since time immemorial. The customary reiterations of the day and night, the yearly cycle of seasons, the shrouds, the tides, the volcanoes, the rainbow have continuously been a source of ponder. The world has an surprising assortment of materials and a befuddling differences of life and conduct. The asking and creative human intellect has reacted to the ponder and wonderment of nature totally different ways. One kind of reaction from the most punctual times has been to watch the physical environment carefully, explore for any significant designs and relations in normal wonders, and construct and utilize unused instruments to connected with nature. This human try driven, in course of time, to advanced science and innovation.

The word Science begins from the Latin verb Scientia meaning ‘to know’. The Sanskrit word Vijñãn and the Arabic word Ilm pass on comparable meaning, specifically ‘knowledge’. Science, in a wide sense, is as ancient as human species. The early civilisations of Egypt, India, China, Greece, Mesopotamia and numerous others made imperative commitments to its advance. From the sixteenth century onwards, awesome strides were made in science in Europe. By the center of the twentieth century, science had ended up a genuinely universal endeavor, with numerous societies and nations contributing to its fast development.

What is Science and what is the so-called scientific method? Science could be a efficient endeavor to get it common marvels in as much detail and profundity as conceivable, and utilize the information so picked up to anticipate, adjust and control marvels. Science is investigating, testing and anticipating from what we see around us. The interest to memorize almost the world, unwinding the privileged insights of nature is the primary step towards the disclosure of science. The logical strategy includes a few interconnected steps : Efficient perceptions, controlled tests, subjective and quantitative thinking, numerical demonstrating, forecast and confirmation or misrepresentation of speculations. Hypothesis and guess too have a put in science; but ultimately, a logical hypothesis, to be satisfactory, must be confirmed by important perceptions or tests. There's much philosophical wrangle about approximately the nature and strategy of science that we require not talk about here.

The transaction of hypothesis and perception (or explore) is fundamental to the advance of science. Science is ever energetic. There's no ‘final’ hypothesis in science and no unchallenged specialist among researchers. As perceptions move forward in detail and exactness or tests surrender modern comes about, speculations must account for them, in case vital, by presenting alterations. Some of the time the adjustments may not be extreme and may lie inside the system of existing hypothesis. For illustration, when Johannes Kepler (1571-1630) inspected the broad information on planetary movement collected by Tycho Brahe (1546-1601), the planetary circular circles in heliocentric hypothesis (sun at the middle of the sun oriented framework) envisioned by Nicolas Copernicus (1473–1543) had to be supplanted by curved circles to fit the information way better. Sometimes, in any case, the existing hypothesis is essentially incapable to clarify unused perceptions.This causes a major change in science. Within the starting of the twentieth century, it was figured it out that Newtonian mechanics, till at that point a really fruitful hypothesis, might not clarify a few of the foremost essential highlights of nuclear wonders. So also, the at that point acknowledged wave picture of light fizzled to clarify the photoelectric impact legitimately. This driven to the improvement of a drastically unused hypothesis (Quantum Mechanics) to bargain with nuclear and atomic marvels.

Fair as a unused explore may propose an elective hypothetical show, a hypothetical development may propose what to hunt for in a few tests. The result of try of scrambling of alpha particles by gold thwart, in 1911 by Ernest Rutherford (1871–1937) set up the atomic show of the iota, which at that point got to be the premise of the quantum hypothesis of hydrogen iota given in 1913 by Niels Bohr (1885–1962). On the other hand, the concept of antiparticle was to begin with presented hypothetically by Paul Dirac (1902–1984) in 1930 and affirmed two a long time afterward by the exploratory revelation of positron (antielectron) by Carl Anderson.

Physics is a basic discipline in the category of Natural Sciences, which also includes other disciplines like 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 describe physics as a study of the basic laws of nature and their manifestation in different natural phenomena. The scope of physics is described briefly in the next section. Here we remark on two principal thrusts in physics : unification and reduction.

In Material science, we endeavor
 to clarify assorted physical marvels in terms of many concepts and laws. The exertion is to see the physical world as appearance of a few widespread laws in numerous spaces and conditions. For case, the same law of attractive energy (given by Newton) depicts the drop of an apple to the ground, the movement of the moon around the soil and the movement of planets around the sun. Essentially, the essential laws of electromagnetism (Maxwell’s conditions) administer all electric and attractive wonders. The endeavors to bind together principal strengths of nature reflect this same journey for unification.

A related exertion is to infer the properties of a greater, more complex, framework from the properties and intuitive of its constituent easier parts. This approach is called reductionism and is at the heart of material science. For case, the subject of thermodynamics, created within the nineteenth century, bargains with bulk frameworks in terms of plainly visible amounts such as temperature, inner vitality, entropy, etc. In this way, the subjects of motor hypothesis and factual mechanics translated these amounts in terms of the properties of the atomic constituents of the bulk framework. In specific, the temperature was seen to be related to the normal motor vitality of particles of the framework.


Able to get a few thought of the scope of material science by looking at its different sub-disciplines. Essentially, there are two spaces of intrigued : plainly visible and minuscule. The plainly visible space incorporates marvels at the research facility, earthly and cosmic scales. The infinitesimal space incorporates nuclear, atomic and atomic marvels*.Classical Material science bargains basically with plainly visible marvels and incorporates subjects like Mechanics, Electrodynamics, Optics and Thermodynamics. Mechanics established on Newton’s laws of movement and the law of attractive energy is concerned with the movement (or harmony) of particles, unbending and deformable bodies, and common frameworks of particles. The impetus of a rocket by a fly of launching gasses, engendering of water waves or sound waves in discuss, the balance of a bowed bar beneath a stack, etc., are issues of mechanics. Electrodynamics bargains with electric and attractive marvels related with charged and attractive bodies. Its essential laws were given by Coulomb, Oersted, Ampere and Faraday, and typified by Maxwell in his celebrated set of conditions.
The movement of a current-carrying conductor in a attractive field, the reaction of a circuit to an ac voltage (flag), the working of an recieving wire, the engendering of radio waves within the ionosphere, etc., are issues of electrodynamics. Optics bargains with the marvels including light. The working of telescopes and magnifying instruments, colours displayed by lean movies, etc., are themes in optics. Thermodynamics, in differentiate to mechanics, does not bargain with the movement of bodies as a entirety. Or maybe, it bargains with frameworks in plainly visible harmony and is concerned with changes in inside vitality, temperature, entropy, etc., of the framework through outside work and exchange of warm. The productivity of warm motors and fridges, the course of a physical or chemical handle, etc., are issues of intrigued in thermodynamics.

scattering experiments of Rutherford gave the nuclear model of the atom.

The tiny space of material science bargains with the structure and structure of matter at the diminutive scales of particles and cores (and indeed lower scales of length) and their interaction with diverse tests such as electrons, photons and other rudimentary particles. Classical material science is insufficient to handle this space and Quantum Hypothesis is as of now acknowledged as the right system for clarifying infinitesimal wonders. In general, the structure of material science is beautiful and forcing and you'll appreciate it more as you seek after the subject.

You'll presently see that the scope of material science is genuinely endless. It covers a huge run of size of physical amounts like length, mass, time, vitality, etc. At one conclusion, it thinks about wonders at the exceptionally little scale of length (10-14 m or indeed less) including electrons, protons, etc.; at the other conclusion, it bargains with galactic wonders at the scale of systems or indeed the whole universe whose degree is of the arrange of 1026 m. The two length scales vary by a figure of 1040 or indeed more. The extend of time scales can be gotten by partitioning the length scales by the speed of light : 10–22 s to 1018 s. The run of masses goes from, say, 10–30 kg (mass of an electron) to 1055 kg (mass of known perceptible universe). Earthbound wonders lie some place within the center of this range.

Point to be noted:- Recently, the domain intermediate between the macroscopic and the microscopic (the so called mesoscopic physics), dealing with a few tens or hundreds of atoms, has emerged as anexciting field of research.

Material science is energizing in numerous ways. To a few individuals the fervor comes from the style and all inclusiveness of its fundamental speculations, from the truth that many fundamental concepts and laws can clarify wonders covering a huge extend of size of physical amounts. To a few others, the challenge in carrying out creative unused tests to open the insider facts of nature, to confirm or invalidate speculations, is exciting. Connected material science is similarly demanding. Application and abuse of physical laws to create valuable gadgets is the foremost curiously and energizing portion and requires incredible inventiveness and tirelessness of exertion.

What lies behind the marvelous
 advance of material science within the final few centuries? Awesome advance as a rule goes with changes in our essential recognitions. To begin with, it was figured it out that for logical advance, as it were subjective considering, though no question vital, isn't sufficient. Quantitative estimation is central to the development of science, particularly material science, since the laws of nature happen to be expressible in exact numerical conditions. The second most imperative knowledge was that the essential laws of material science are widespread — the same laws apply in broadly distinctive settings. In conclusion, the procedure of estimation turned out to be exceptionally effective. Most watched marvels in standard of living are or maybe complicated signs of the fundamental laws. Researchers perceived the significance of extracting the basic features of a phenomenon from its less critical perspectives. It isn't commonsense to require under consideration all the complexities of a marvel in one go. A great methodology is to center to begin with on the basic highlights, find the fundamental standards and after that present adjustments to construct a more refined hypothesis of the marvel. For case, a stone and a quill dropped from the same tallness don't reach the ground at the same time. The reason is that the fundamental perspective of the wonder, to be specific free drop beneath gravity, is complicated by the nearness of air resistance. To induce the law of free drop beneath gravity, it is way better to form a circumstance wherein the discuss resistance is unimportant. Able to, for illustration, let the stone and the feather drop through a long emptied tube. In that case, the two objects will drop nearly at the same rate, giving the fundamental law that speeding up due to gravity is free of the mass of the protest. With the fundamental law hence found, ready to go back to the quill, present redresses due to discuss resistance, adjust the existing hypothesis and attempt to construct a more practical hypothesis of objects falling to the soil beneath gravity.

Hypothesis, axioms and models

One ought to not think that everything can be demonstrated with material science and science. All material science, conjointly science, is based on presumptions, each of which is differently called a theory or maxim or hypothesize, etc.

For case, the widespread law of attractive energy proposed by Newton is an presumption or speculation, which he proposed out of his inventiveness. Some time recently him, there were a few perceptions, tests and information, on the movement of planets around the sun, movement of the moon around the soil, pendulums, bodies falling towards the soil etc. Each of these required a isolated clarification, which was more or less subjective. What the all inclusive law of attraction says is that, in case we expect that any two bodies within the universe draw in each other with a drive relative to the item of their masses and contrarily corresponding to the square of the distance between them, at that point we are able clarify all these perceptions in one stroke. It not as it were clarifies these marvels, it too permits us to anticipate the comes about of future tests.

A theory may be a supposition without expecting that it is genuine. It would not be reasonable to inquire anyone to demonstrate the all inclusive law of attraction, since it cannot be demonstrated. It can be confirmed and substantiated by tests and perceptions.

An maxim may be a self-evident truth whereas a show could be a hypothesis proposed to clarify watched marvels. But you wish not stress at this arrange almost the subtleties in utilizing these words. For example, another year you'll learn almost Bohr’s show of hydrogen iota, in which Bohr accepted that an electron within the hydrogen iota takes after certain rules (postutates). Why did he do that? There was a large amount of spectroscopic information some time recently him which no other hypothesis seem clarify. So Bohr said that on the off chance that we accept that an particle carries on in such a way, we are able clarify all these things at once.

Einstein’s extraordinary hypothesis of relativity is additionally based on two hypothesizes, the steadiness of the speed of electromagnetic radiation and the legitimacy of physical laws in all inertial outline of reference. It would not be astute to inquire someone to demonstrate that the speed of light in vacuum is consistent, autonomous of the source or spectator.

In arithmetic as well, we require adages and theories at each arrange. Euclid’s explanation that parallel lines never meet, could be a speculation. This means that on the off chance that we expect this explanation, ready to clarify a few properties of straight lines and two or three dimensional figures made out of them. But in the event that you don’t accept it, you're free to utilize a distinctive adage and get a modern geometry, as has in fact happened within the past few centuries and decades.


The association between material science, innovation and society can be seen in numerous illustrations. The teach of thermodynamics emerged from the got to get it and progress the working of warm motors. The steam motor, as we know, is indistinguishable from the Mechanical Insurgency in Britain within the eighteenth century, which had awesome affect on the course of human civilisation. In some cases innovation gives rise to unused material science; at other times material science produces modern innovation. An illustration of the last mentioned is the remote communication technology that taken after the disclosure of the fundamental laws of power and attraction within the nineteenth century. The applications of material science are not continuously simple to predict. As late as 1933, the extraordinary physicist Ernest Rutherford had expelled the plausibility of tapping vitality from particles. But as it were some a long time afterward, in 1938, Hahn and Meitner found the marvel of neutron-induced parting of uranium, which would serve as the premise of atomic control reactors and atomic weapons. However another vital case of material science giving rise to innovation is the silicon ‘chip’ that activated the computer insurgency within the final three decades of the twentieth century. A most noteworthy range to which material science has and will contribute is the improvement of elective vitality resources. The fossil powers of the planet are decreasing quick and there's an critical got to find unused and reasonable sources of vitality. Impressive advance has as of now been made in this heading (for illustration, in change of sun powered vitality, geothermal vitality, etc., into power), but much more is still to be fulfilled.

Physics is the study of nature and natural phenomena. Physicists try to discover the rules that are operating in nature, on the basis of observations, experimentation and analysis. Physics deals with certain basic rules/laws governing the natural world.

What is the Nature of physics? We will discuss next........

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