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# NCERT Solutions for class 11 Physics chapter 1 Physical world PDF - eSaral

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### Download NCERT Solutions for class 11 Physics chapter 1 Physical world PDF"

Question 1. Some of the most profound statements on the nature of science have come from Albert Einstein, one of the greatest scientists of all time. What do you think did Einstein mean when he said: "The most incomprehensible thing about the world is that it is comprehensible"?

Solution: Naturally, the entire physical world is complicated. The biological world has its own complexities. Moreover, space, time and mass are involved in different orders of magnitudes. Despite, of all this, almost all the physical phenomena can be expressed in terms of a few basic laws. In this context, the statement made by Einstein becomes very evident.

Question 2. “Every great physical theory starts as a heresy and ends as a dogma”. Give some examples from the history of science of the validity of this incisive remark

Solution: In our daily lives, a common observation is that light travels in a straight line. It was heresy when Huygens advocated his theory of waves. However, it quickly became a dogma that could be explained effectively on the grounds of wave theory as interference patterns, refraction, etc.
The light was believed to be only energy, but when the photoelectric effect was discovered, it was proposed that light had a particle nature, this was widely debated and treated as hearsay. However, Einstein finally proved it with his quantum theory of light. Henceforth, it has been regarded as a dogma

Question 3. “Politics is the art of the possible”. Similarly, “Science is the art of the soluble”. Explain this beautiful aphorism on the nature and practice of science.

Solution: Politicians make everything possible to win votes. And science is a systematized study of observation. Researchers and scientist study these observations and then work out certain laws from them. In this universe, there are several natural phenomena taking place and all of them can be described in terms of some basic laws. For example, F = mg is valid for you and me and also for a star. Thus, we see in science that different phenomena are related, they are soluble and can be clarified with the same or similar law. This continues to justify that science is the art of the soluble just as politics is the art of the possible.

Question 4. Though India now has a large base in science and technology, which is fast expanding, it is still a long way from realizing its potential of becoming a world leader in science. Name some important factors, which in your view have hindered the advancement of science in India.

Solution: Here are some significant factors that have hindered scientific development in India: lack of infrastructure and funding for high-quality scientific research work education in science is neither correctly oriented nor guided. Depending on our demands, it requires particular directions.
Industrialists are the real consumers of new technology and research. The industrialists of this country have little confidence in the ability of Indian scientists. There is practically no coordination between scientists and industrialists. Rural science schooling is almost non-existent so that the majority of the population is deprived of the advantages of technology and science advances poor pay scales and other facilities for researchers compared to administrators

Question 5. No physicist has ever “seen” an electron. Yet, all physicists believe in the existence of electrons. An intelligent but superstitious man advances this analogy to argue that ‘ghosts’ exist even though no one has ‘seen’ one. How will you refute his argument?

Solution: Although an electron was never ‘seen’ its impacts were observed and its practical evidence was tested and proven. For example, electricity. With respect to spirits and ghosts, though there are many claims and sightings, standardized scientific reading and evidence have never been observed or tested successfully. So, we can't really say that they exist with cent percent surety

Question 6. he shells of crabs found around a particular coastal location in Japan seem mostly to resemble the legendary face of a Samurai. Given below are two explanations of this observed fact. Which of these strikes you as a scientific explanation?

(a) A tragic sea accident several centuries ago drowned a young Samurai. As a tribute to his bravery, nature through its inscrutable ways immortalized his face by imprinting it on the crab shells in that area
(b) After the sea tragedy, fishermen in that area, in a gesture of honor to their dead hero, let free any crab shell caught by them which accidentally had a shape resembling the face of a Samurai. Consequently, the particular shape of the crab shell survived longer and therefore in course of time the shape was genetically propagated. This is an example of evolution by artificial selection.
[Note: This interesting illustration taken from Carl Sagan’s ‘The Cosmos’ highlights the fact that often strange and inexplicable facts which on the first sight appear ‘supernatural’ actually turn out to have simple scientific explanations. Try to think out other examples of this kind].

Solution: Explanation (b) More logical and scientific.

Question 7. The industrial revolution in England and Western Europe more than two centuries ago was triggered by some key scientific and technological advances. What were these advances?

Solution: Some of the main developments in science and technology during this era include:
(1) The use of heat and thermodynamics to form the steam engine.
(2) Electricity discovery and implementation helped to create motors and dynamos.
(3) Study of gravitation led to the study of motion and making cannons and guns. This gave Western countries authority in their hands, and they ruled the rest of the world.
(4) The discovery of explosives helped not only the military but mineral exploration as well. These are some instances of improvements in science and technology that helped England and Europe gain prominent positions in the world.
(5) The advances in chemistry, physics and natural sciences actually introduced the industrial revolution in Western Europe and England.

Question 8. It is often said that the world is witnessing now a second industrial revolution, which will transform the society as radically as did the first. List some key contemporary areas of science and technology, which are responsible for this revolution.

Solution: Some of the key contemporary areas of technology and science that are now mainly responsible for a new industrial revolution and are likely to occur in the near future are:
(1) Design of Super-fast computers using artificial intelligence.
(2) Biotechnology.
(3) Development at room temperature of superconducting materials.
(4) Advances in the field of tech electronics, including information technology as well as nanotechnology.
(5) Developments in the space sciences sector.

Question 9. Write in about 1000 words a fiction piece based on your speculation on the science and technology of the twenty-second century.

Solution: Imagine that you are in a spaceship, along with your friends, moving towards Mars. The spaceship's body is made of a specially constructed material that gets hard as its temperature increases. This spacecraft uses nuclear fuel and three nuclear power plants which are located in a spacecraft. Alternatively, two of them operate and the third is for an emergency. The spaceship's speed is very high and you're all very pleased. The energy generated in power plants is transformed into electrical energy which runs the motors of the spaceship. You reach Mars securely together with your friends, collect information, take pictures, and then return to earth. The spacecraft collides with an object in space on the return trip because of which two power plants stop working. Now only one power plant is in operation and its efficiency is continuously declining owing to overheating. By flowing air in the plant, you and your friends attempt to decline the temperature of the power plant and attempt to repair the fuse of the other power plants. Finally, one other plant's fuse is repaired and begins to operate before the first plant crosses the danger limit of an excess of temperature. You and your friends are finally returning to Earth securely.

Question 10. Attempt to formulate your ‘moral’ views on the practice of science. Imagine yourself stumbling upon a discovery, which has great academic interest but is certain to have nothing but dangerous consequences for the human society. How, if at all, will you resolve your dilemma?

Solution: A scientist works for the truth. Every scientific discovery reveals a certain truth of nature. Any discovery, bad or good for humanity, must, therefore, be made public. But we can't afford to be blind to the consequences. We need to determine the degree of good or bad consequences it will have before disclosing it. If we know that a certain discovery has nothing but dangerous consequences to offer to the mass, it is best to keep the discovery limited only to the scientist's knowledge and researcher's working on it. In the long run, the discovery can benefit societies without destroying it completely now.

Question 11. Science, like any knowledge, can be put to good or bad use, depending on the user. Given below are some of the applications of science. Formulate your views on whether the particular application is good, bad or something that cannot be so clearly categorized:
(a) Mass vaccination against small pox to curb and finally eradicate this disease from the population. (This has already been successfully done in India).
(b) Television for eradication of illiteracy and for mass communication of news and ideas.
(c) Prenatal sex determination.
(d) Computers for increase in work efficiency.
(e) Putting artificial satellites into orbits around the Earth.
(g) Development of new and powerful techniques of chemical and biological warfare).
(h) Purification of water for drinking
(i) Plastic surgery
(j) Cloning
(f) Development of nuclear weapons

Solution: (a) So many human beings and survivors are killed by the smallpox virus. Thus, smallpox mass vaccination is good for society
(b) Television for the eradication of literacy and for mass communication of news and ideas is good.
(c) Determination of parental sex is considered bad as it leads to gender imbalance and is legally banned in many countries.
(d) Computers are helpful in effectively and efficiently doing a job. It leads to globalization and improves connectivity among individuals all over the globe. Computers are therefore considered to be good.
(e) The launch of artificial satellites is good because this artificial satellite is based on the internet, television, a Global Positioning System (GPS) and many other bridges between human across the great seas are based on this artificial satellite.
(f) Although nuclear physics development leads to efficient electricity generations, it is considered to be bad. Because it causes the destruction of human colonies during wars, inserts permanent changes in living genes and causes changes in the environment
(g) It is bad to develop new and powerful chemical and biological warfare methods. Terrorists, anti-government societies, etc. can just misuse it.
(h) It is good to purify drinking water. It's the main problem we face nowadays.
(i) It is considered that plastic surgery is good. Because it provides new life to acid drop victims, fire accidents, and many others.
(j) It is not possible to categorize cloning. Because reproducing new organs using cloning is good, but the entire human being's development leads to so many social and security problems

Question 12. India has had a long and unbroken tradition of great scholarship — in mathematics, astronomy, linguistics, logic and ethics. Yet, in parallel with this, several superstitious and obscurantist attitudes and practices flourished in our society and unfortunately continue even today — among many educated people too. How will you use your knowledge of science to develop strategies to counter these attitudes?

Solution: Poverty and illiteracy are the two main factors that make people in India superstitious. So, we must first overcome these factors in order to remove the superstitious and obscurantist attitudes. To be able to have a scientific approach, everyone should be educated. Knowledge of science can be used to prove the superstition of people wrong by showing them the logic behind everything that happens in the world.

Question 13. Though the law gives women equal status in India, many people hold unscientific views on a woman’s innate nature, capacity and intelligence, and in practice give them a secondary status and role. Demolish this view using scientific arguments, and by quoting examples of great women in science and other spheres; and persuade yourself and others that, given equal opportunity, women are on par with men.

Solution: There is no difference in the ability of women and men as far as work, intelligence, decision making is concerned. Nature makes little difference in the anatomy and feeling of men and women. Prenatal and postnatal diet nutritional content contributes significantly to the development of a human body. If women and men are given equal opportunities, the female mind and body will be just as efficient as a man. The list of great women who have excelled in their respective fields is enormous. Names of Madam Curie, Indira Gandhi, Florence Nightingale, Margaret Thatcher, Mother Teresa, Sarojini Naidu, Kalpana Chawla, been taken from fields varying from sociology to science and they all very well-known for their contribution to the world.

Question 14. “It is more important to have beauty in the equations of physics than to have them agree with experiments”. The great British physicist P. A. M. Dirac held this view. Criticize this statement. Look out for some equations and results in this book which strike you as beautiful.

Solution: The belief of Driac is true. Equations representing entire concepts and hold up against experimental results are automatically simple, small and symmetrical, making them genuinely beautiful. Some beautiful equations are:
$\mathrm{E}=\mathrm{mc}^ {2}$ (Energy of Light)
$\mathrm{E}=\mathrm{hv}$ (Energy of Photon)
$\mathrm{W}=$ F.d (Work done)
P. $\mathrm{E}=\mathrm{mgh}$. (Potential energy of a body at rest)
All equations have the same dimensions. One equation shows the dependency of Energy on frequency and displacement and the other shows the dependency of Energy on speed. That is the beauty of equations coming in Physics from different experiments.

Question 15. Though the statement quoted above may be disputed, most physicists do have a feeling that the great laws of physics are at once simple and beautiful. Some of the notable physicists, besides Dirac, who have articulated this feeling, are Einstein, Bohr, Heisenberg, Chandrasekhar and Feynman. You are urged to make special efforts to get access to the general books and writings by these and other great masters of physics. (See the Bibliography at the end of this book.) Their writings are truly inspiring!

Solution: It is completely true that the great laws of Physics are simple and beautiful: Few examples are given below:
(i) Einstein's mass-energy equivalence is simple and beautiful.
(ii) According to Max Planck's quantum, the energy of a Photon is E = h𝜈, is also simple and beautiful.
(iii) De- Broglie wavelength associated with a Particle of mass $\mathrm{m}$ is given by $\lambda=\frac{h}{m \cdot v} .$ It is also simple and beautiful

Question 16. Textbooks on science may give you a wrong impression that studying science is dry and all too serious and that scientists are absent-minded introverts who never laugh or grin. This image of science and scientists is patently false. Scientists, like any other group of humans, have their share of humorists, and many have led their lives with a great sense of fun and adventure, even as they seriously pursued their scientific work. Two great physicists of this genre are Gamow and Feynman. You will enjoy reading their books listed in the Bibliography

Solution: It is true that scientists have their share of humorists like any other group of humans. Gamow and Feynman are two excellent physicists of this genre. CV Raman, Einstein, Bohr, former Indian President APJ Abdul Kalam, etc. are just a few other scientists whose name can be added to this list.

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