NCERT Solutions: Physical World - Notes | Study Physics Class 11 - NEET

Q.1.1. 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”?

Albert Einstein

Ans.  The whole of the physical world around us is very complex in nature because of the occurrence of millions of phenomena. The biological world has its own complexities. So the world seems incomprehensible i e. as if it cannot be understood. Moreover, we come across wide ranges of mass, length and time which surprisingly be understood and expressed in terms of few basic laws. In other words, the complex nature of the physical world from atomic to astronomical ranges can be understood in terms of a few basic concepts, so the physical world becomes comprehensible. When viewed in this context, Einstein's admiration becomes very clear.

Q.1.2. “Every great physical theory starts as a heresy and ends as a dogma”. Give some examples from the history of the science of the validity of this incisive remark.
Ans. The statement above is true. The validity of this incisive remark can be validated from the example of a moment of inertia. It states that the moment of inertia of a body depends on its energy. But according to Einstein's mass-energy relation (E = mc²), energy depends on the speed of the body.

For Example: 

(i) Thomas Young's wave theory of light started as a heresy and finally ended as 'dogma' when Einstein and other replaced it by quantum theory of light.

(ii) In ancient times, Ptolemy postulated that earth is stationary and all the heavenly bodies like sun, stars, planets etc. revolve around it. Later, an Italian scientist Galileo postulated that sun is stationary and earth along with other planets is revolving around the sun. Galileo was punished by the then authorities for spreading wrong concepts. But later on Newton and Kepler supported Galileo's theory and now it is a dogma.

(iii) There was an heresy that inertia of a body depends upon its energy. Einstein put forth a single equation relating mass and energy which is called as mass-energy equivalence relation (E = mc²) and this is a dogma in Physics.

Q.1.3. "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.
Ans.  

• It is a well-known fact that to win over votes, politicians make anything and everything possible even when they are least sure of the same. 
• Science is a systematised study of observations. A scientist patiently analyses these observations and comes out with certain laws.
  Example: Tycho Brahe worked for twenty long years to make observations on planetary motions. J. Kepler formulated his three famous laws of planetary motion from this huge reservoir of observations. Thus, the statement that science is the art of the soluble means that a wide variety of physical processes are understood in terms of only a few basic concepts i.e., there appears to be unity in diversity as if widely different phenomena are soluble and can be explained in terms of only a few fundamental laws.

Q.1.4. 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.
Ans. Some important factors in our view which have hindered the advancement of science in India are:

• Proper funds are not arranged for the development of research work and laboratories. The labs and scientific instruments are very old and outdated.

Old scientific instruments

• Most of the people in India are uneducated and highly traditional. They don't understand the importance of Science.
• There is no proper employment opportunity for the science-educated person in India.
• There are no proper facilities for science education in schools and colleges in India.

Q.1.5. 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?

Ans. Even though an electron has never been ‘seen’ but its effects have been observed and its practical evidence has been tested and proved.

Example: Electricity

However, regarding spirits and ghosts, even though there are many claims and sightings, standardized scientific reading and evidence have never been observed or successfully tested. Thus, we really cannot state with a cent percent surety that they exist.

Q.1.6. The 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 is taken from Carl Sagan’s ‘The Cosmos’ highlights the fact that often strange and inexplicable facts which at first sight appear ‘supernatural’ actually turn out to have simple scientific explanations. Try to think out other examples of this kind].

Ans. Explanation (b) is correct is a scientific explanation of the observed fact as it is backed by the scientific theory of 'evolution by artificial selection'.

Q.1.7. 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?

Ans. More than two centuries ago, England and Western Europe invented the steam engine, electricity, the theory of gravitation, and explosives. Steam engines helped them in the field of heat and thermodynamics, the theory of gravitation in the field of motion, and making guns and cannons. This progress brought about the industrial revolution in England and Western Europe.

Q.1.8. It is often said that the world is witnessing now a second industrial revolution, which will transform society as radically as did the first. List some key contemporary areas of science and technology, which are responsible for this revolution.

Ans. Some of the key contemporary areas of science and technology which may transform society radically are:

• Development of super-fast computers.
• The Internet and tremendous advancement in information technology.
• Development in Biotechnology.
• Development of superconducting materials at room temperature.
• Development of robots.

Q.1.9. Write in about 100 words a fiction piece based on your speculation on the science and technology of the twenty-second century.
Ans. Let me take into the year A.D. 2125. Human colonies are developed on Mars and the moon. One day evening a mysterious asteroid driven by aliens coming towards our colonies, then International Space Soldiers Army (ISSA) which is developed by all the nations has come into the picture. They pointed a multi satellite-based Laser gun (MSLG) towards it and destroyed the asteroid. This MSLG is working with the radiation coming from the sun, it has a debris collector inbuilt and it requires no other source of energy.

Q.1.10. 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 human society. How, if at all, will you resolve your dilemma?

Ans. In our view, a type of discovery that is of great academic interest but harmful for human society should not be made public because Science is for society, society is not for science.

Q.1.11. 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:
Ans. 

• Mass vaccination against smallpox to curb and finally eradicate this disease from the population. (This has already been successfully done in India). Good, Mass vaccination helped eradicate the dreaded diseases from the Earth.

Mass vaccination

• Television for the eradication of illiteracy and for mass communication of news and ideas. Good, Television helps in the literacy campaign and is an effective method of mass communication and entertainment.
• Prenatal sex determination - Bad, Prenatal sex determination is considered bad because it gives rise to the practice of abortion in the case of the female fetus.
• Computers for the increase in work efficiency - Good, Computer increases work efficiency.
• Putting artificial satellites into orbits around the Earth - Good, Artificial satellites help in the worldwide communication process.
• Development of nuclear weapons - Bad, Nuclear weapons if misused may cause mass destruction of mankind.
• Development of new and powerful techniques of chemical and biological warfare - Bad, These techniques may be misused for destructive purposes.
• Purification of water for drinking - Good, Purified water improves the health of people.
• Plastic surgery - Neither good nor bad. Plastic surgery is something that can’t be classified as either good or bad because it helps to remove a certain type of deformations in needy persons.
• Cloning - Good, Cloning has the potential to ruin the normal family life of human society.

Q.1.12. 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?
Ans. Poverty and illiteracy are the two major factors that make people superstitious in India.

• So to remove the superstitious and obscurantist attitude we have to first overcome these factors. 
• Everybody should be educated so that one can have a scientific attitude. 
• Knowledge of science can be put to use to prove people's superstitious wrong by showing them the scientific logic behind everything happening in our world.

Q.1.13. 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.
Ans. Some people in our society have the view that women do not have the innate nature, capacity, and intelligence.  To demolish this view there are many examples of women who have proven their abilities in Science and other fields. Madame Curie, Mother Teresa, Indira Gandhi, Margaret Thatcher, Rani Laxmi Bai, Florence Nightingale are some examples. So in this era, women are definitely not behind the man in any field.

Q.1.14. “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 that strike you as beautiful.
Ans. An equation that agrees with an experiment must also be simple and hence beautiful. We have some simple and beautiful equations in Physics such as:

• E = mc² (Energy of light)
• E = hν (Energy of a photon)
• KE = 1/2 mv² (Kinetic energy of a moving particle)
• PE = mg (Potential energy of a body at rest)
• W = F.d (Work done)

All have the same dimensions. One experiment shows the dependency of energy on speed, the other shows dependency on frequency & displacement. That's the beauty of equations in Physics coming from different experiments.