Tagore Vidhya Pith H. S. School Study Material:- 2020–21 Class:-11th Subject:- Physics . Chapter:- 1 Introduction Answer the following questions- Q1) What do you mean by Science? Ans- Science → The word „science‟ has been derived from the Latin verb „scientia‟ which means „to know‟. This knowledge gained by men through systematic and organized observation and experiments, is called science. For the convenience science is divided in two main branches : 1) Physical science → The branch of science which includes the study of subjects like physics, chemistry, mathematics, geology, astronomy etc. is called physical science. 2) Biological science → The branch of science which includes the study of subjects like Botany, zoology etc. is called biological science. Q2) What is Physics? Ans- Physics → Physics is a branch of science which deals with the study of basic laws of nature and natural phenomena. OR “The branch of science in which the properties of matter, energy and their interactions are studied.” Q3) What is Matter? Ans- Matter → It is something that has a mass, occupies space and can be felt with our sense organs. For example : Iron, air, wood etc. Matter is of three types : 1) Solids, 2) Liquids and 3) Gases. 1) Solids → These are the substances which possess finite shape and volume both. 2) Liquids → These substances have definite volume but there shape is not finite. 3) Gases → These substances do not have definite shape and definite volume. Q4) What are the branches of physics? Ans- Physics has been classified into two categories : 1) Classical physics and 2) Modern physics. 1) Classical physics → The physics developed before 1900 on the basis of systematic and organized knowledge is called classical physics. The branches of classical physics are : (i) Mechanics → It is the oldest branch of physics. It includes the study of stationary and slow moving (speed less than the speed of light) bodies. (ii) Thermodynamics → This branch of physics is related with the concept of heat and temperature. (iii) Optics → This branch of physics includes the study of light energy and phenomena related with light. www.tagorevidhyapith.com Tagore Vidhya Pith H. S. School (iv) Electromagnetism → This branch of physics deals with the study of electricity, magnetism and electromagnetic radiations. 2) Modern physics → The physics developed after 1900 is called modern physics. It includes the study of fundamental particles, atom, nucleus, condensed matter, theory of relativity and quantum mechanics. Following are the main branches of modern physics : (i) Theory of relativity → It deals with the study of motion of particles moving with speeds of the order of speed of light. Albert Einstein formulated the special theory of relativity. (ii) Quantum mechanics → It includes the study of sub-microscopic particles, principles of modern physics, Light and dual nature of light. (iii) Atomic physics → It includes the study of atomic structure and characteristics of atom. (iv) Nuclear physics → It deals with the study of structure and characteristics of nucleus of atom. (v) Solid state physics → This branch deals with the study of crystalline substances, characteristics and uses of semiconductors and alloys. (vi) Electronics → It deals with the study of devices based on the properties of electron and applications of these devices. Q5) What are the nature of physical laws? Ans- Scientific Attitude → The philosophy developed on the basis of logics and experimental facts is called scientific attitude. Hypothesis → The working laws initially formulated but have not finally verified and are used to explain the observations or experimental results are called hypothesis. Scientific law → The general statements which tells about the behaviour of nature are called scientific laws. Theory → Hypothesis developed on the basis of some known laws to explain the behaviour of physical systems is called „theory‟. Q6) Explain forces in nature. Ans- Forces in Nature → Force is an external agent which produces a change or tends to produce a change in the state of rest, state of motion or shape and size of a body. Following are the four fundamental forces that exist in nature : 1) Gravitational force 2) Electromagnetic force 3) Strong nuclear force 4) Weak nuclear force 1) Gravitational force → The force acting between different bodies in the universe is called gravitational force. Characteristics : (i) This force obeys the inverse square law. (According to inverse square law force acting between two bodies varies inversely with the square of distance between them). (ii) Gravitational force is always attractive. (iii) It is a long range force. It exists up to infinite distance. Thus, it is a long range force. (iv) It is the weakest force. It plays important role at macroscopic level. www.tagorevidhyapith.com Tagore Vidhya Pith H. S. School 2) Electromagnetic force → The force between two charged bodies is called electrostatic force and the force between two magnets is called magnetic force. Characteristics : (i) It obeys inverse square law. (ii) This force may be attractive or repulsive. 36 (iii) Electrostatic force between two protons placed certain distance is 10 times stronger than the gravitational force between two proton lying at same distance. 3) Strong Nuclear forces → Strong nuclear force is that which keeps the nucleus inside the nucleus. Characteristics : (i) It does not obey the inverse square law. (ii) This force is an attractive force. -15 (iii) It is a short range force (of the order of 10 m). 38 (iv) This force is 100 times stronger than the electromagnetic force and 10 times stronger than the gravitational force. 4) Weak Nuclear forces → It is that force which acts between the fundamental particles, emitted during the radioactive decay of elements/materials. Characteristics : (i) Weak nuclear force is stronger than the gravitational force but very weak than the electromagnetic and strong nuclear forces. (ii) It is a short range force (of the order of 10-16 m). Q7) Write some technological innovations and the relevant physical principles. Ans- In the table below are given some of the technological innovations and the relevant physical principles : Technological innovation Principle 1. Electric generator 1. Faraday‟s laws of electromagnetic induction. 2. Computer 2. Digital logic of electronic circuits. 3. Genetic Engineering 3. Role of DNA in genetics. 4. Aeroplane 4. Bernoulli‟s theorem in hydrodynamics. 5. Particle accelerator 5. Motion of charged particles in electric and magnetic fields. 6. Radio, Television and Telecommunication 6. Transmission of electromagnetic waves. 7. Nuclear reactor 7. Fission of Uranium atom by slow moving neutrons. 8. Rocket propulsion, launching of artificial 8. Newton‟s laws of motion. satellite and space craft. 9. Hydroelectric energy 9. Conversion of gravitational energy into electrical energy. 10. Laser 10. Amplification by population inversion. 11. Production of very high magnetic field. 11. Super conductivity. 12. Heat engine, Air-conditioning, Refrigerator. 12. Laws of thermodynamics. www.tagorevidhyapith.com .