Class 11 Physics

Physical World

Science: “Science is a systematic attempt to understand natural phenomena in as much detail and depth as possible, and use the knowledge so gained to predict, modify and control phenomena.”

Physics: The study of the basic laws of nature and their manifestation in different natural phenomena is called physics.

Gravitational Force: The force of mutual attraction between any two objects by virtue of their masses is called gravitational force. It is a universal force, i.e. every object in the universe experiences this force due to every other object in the universe.

Electromagnetic Force: The force between charged bodies is called electromagnetic force. Both gravitational force and electromagnetic force act over large distances and do not need a medium to do so. Compared to gravitational force, the electromagnetic force is enormously strong. For example; the electromagnetic force between two protons is 1036 times than gravitational force for a given distance. Gravity is always attractive but electromagnetic force can be either attractive or repulsive.

Strong Nuclear Force: The force that binds protons and neutrons in a nucleus is called strong nuclear force. The strong nuclear force is the strongest of all fundamental forces. It is about 100 times the electromagnetic force in strength. It is independent of charge and acts equally between a proton and a proton, a neutron and a neutron, and a proton and a neutron. The range of strong nuclear force is extremely small, of about nuclear dimensions (10-15 m). It is important to note that electrons do not experience this force.

Weak Nuclear Force: This force appears only in certain nuclear processes, e.g. the β-decay of a nucleus. This force is stronger than gravitational force but much weaker than strong nuclear force and electromagnetic force. The range of weak nuclear force is exceedingly small, of the order of 10–16 m.


Questions 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”?

Answer: The world is so vast that it is impossible to comprehend everything about it by an individual. There are trillions of celestial bodies in the universe and till date we know only about a small fraction of it. There is a huge variety of living beings on this planet but we know about a minuscule portion of it. However, we have devised various means to understand the vastness of our world. For example; we can explain various natural phenomena on the basis of universal law of gravitation. So, I think Einstein had correctly said that the most incomprehensible thing about the world is that it is comprehensible.

Questions 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.

Answer: A heresy is defined as a belief or opinion that is contrary to orthodox religious doctrine. A dogma is a principle or a set of principles, laid down by an authority as incontrovertibly true. When Nicolaus Copernicus first came up with the theory that the earth revolves around the sun, it was a heresy because the common belief at that time was the other way round. After observational proofs by Copernicus and other scientists, it was proved that the earth indeed moves around the sun. Today, is has become a dogma because it is an established fact and nobody finds it unbelievable.

Questions 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.

Answer: In the field of science, one theory leads to another. Principles of science obey each other. For example; theory of relativity can explain so many things. Similarly, universal law of gravitation can explain the planetary motion and can also help in sending a man to the moon. So, it can be said that science is the art of the soluble.

Questions 4: Though India now has a large base in science and technology, which is fast expanding, it is still a long way from realising 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.

Answer: Following are some factors which have hindered the advancement of science in India: