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PHYSICS HIGHER SECONDARY SECOND YEAR VOLUME - I Revised based on the recommendation of the Textbook Development Committee Untouchability is a sin Untouchability is a crime Untouchability is inhuman TAMILNADU TEXTBOOK CORPORATION COLLEGE ROAD, CHENNAI - 600 006c Government of Tamilnadu First edition - 2005 Revised edition - 2007 CHAIRPERSON Dr. S. GUNASEKARAN Reader Post Graduate and Research Department of Physics Pachaiyappa’s College, Chennai - 600 030 Reviewers S. RASARASAN P . SARVAJANA RAJAN Selection Grade Lecturer in Physics P.G. Assistant in Physics Govt. Hr. Sec. School Govt.Arts College Nandanam, Chennai - 600 035 Kodambakkam, Chennai - 600 024 S. KEMASARI GIRIJA RAMANUJAM Selection Grade Lecturer in Physics P.G. Assistant in Physics Queen Mary’s College (Autonomous) Govt. Girls’ Hr. Sec. School Chennai - 600 004 Ashok Nagar, Chennai - 600 083 Dr. K. MANIMEGALAI Reader in Physics P. LOGANATHAN The Ethiraj College for Women P.G. Assistant in Physics Chennai - 600 008 Govt. Girls’ Hr. Sec. School Tiruchengode - 637 211 G. SANKARI Namakkal District Selection Grade Lecturer in Physics Meenakshi College for Women Dr. N. VIJAYAN Kodambakkam, Chennai - 600 024 Principal G. ANBALAGAN Zion Matric Hr. Sec. School Selaiyur Lecturer in Physics Aringnar Anna Govt. Arts College Chennai - 600 073 Villupuram. Dr. HEMAMALINI RAJAGOPAL Authors Senior Scale Lecturer in Physics Queen Mary’s College (Autonomous) S. PONNUSAMY Chennai - 600 004 Asst. Professor of Physics S.R.M. Engineering College S.R.M. Institute of Science and Technology (Deemed University) Kattankulathur - 603 203 Price : Rs. This book has been prepared by the Directorate of School Education on behalf of the Government of Tamilnadu This book has been printed on 60 G.S.M paper Printed by offset at :Preface The most important and crucial stage of school education is the higher secondary level. This is the transition level from a generalised curriculum to a discipline-based curriculum. In order to pursue their career in basic sciences and professional courses, students take up Physics as one of the subjects. To provide them sufficient background to meet the challenges of academic and professional streams, the Physics textbook for Std. XII has been reformed, updated and designed to include basic information on all topics. Each chapter starts with an introduction, followed by subject matter. All the topics are presented with clear and concise treatments. The chapters end with solved problems and self evaluation questions. Understanding the concepts is more important than memorising. Hence it is intended to make the students understand the subject thoroughly so that they can put forth their ideas clearly. In order to make the learning of Physics more interesting, application of concepts in real life situations are presented in this book. Due importance has been given to develop in the students, experimental and observation skills. Their learning experience would make them to appreciate the role of Physics towards the improvement of our society. The following are the salient features of the text book. N The data has been systematically updated. N Figures are neatly presented. N Self-evaluation questions (only samples) are included to sharpen the reasoning ability of the student. While preparing for the examination, students should not restrict themselves, only to the questions/problems given in the self evaluation. They must be prepared to answer the questions and problems from the text/syllabus. – Dr. S. Gunasekaran Chairperson IIISYLLABUS (180 periods) UNIT – 1 ELECTROSTATICS (18 periods) Frictional electricity, charges and their conservation; Coulomb’s law – forces between two point electric charges. Forces between multiple electric charges – superposition principle. Electric field – Electric field due to a point charge, electric field lines; Electric dipole, electric field intensity due to a dipole –behavior of dipole in a uniform electric field – application of electric dipole in microwave oven. Electric potential – potential difference – electric potential due to a point charge and due a dipole. Equipotential surfaces – Electrical potential energy of a system of two point charges. Electric flux – Gauss’s theorem and its applications to find field due to (1) infinitely long straight wire (2) uniformly charged infinite plane sheet (3) two parallel sheets and (4) uniformly charged thin spherical shell (inside and outside) Electrostatic induction – capacitor and capacitance – Dielectric and electric polarisation – parallel plate capacitor with and without dielectric medium – applications of capacitor – energy stored in a capacitor. Capacitors in series and in parallel – action of points – Lightning arrester – Van de Graaff generator. UNIT - 2 CURRENT ELECTRICITY (11 periods) Electric current – flow of charges in a metallic conductor – Drift velocity and mobility and their relation with electric current. Ohm’s law, electrical resistance. V-I characteristics – Electrical resistivity and conductivity. Classification of materials in terms of conductivity – Superconductivity (elementary ideas) – Carbon resistors – colour code for carbon resistors – Combination of resistors – series and parallel – Temperature dependence of resistance – Internal resistance of a cell – Potential difference and emf of a cell. Kirchoff’s law – illustration by simple circuits – Wheatstone’s Bridge and its application for temperature coefficient of resistance measurement – Metrebridge – Special case of Wheatstone bridge – Potentiometer – principle – comparing the emf of two cells. Electric power – Chemical effect of current – Electro chemical cells Primary (Voltaic, Lechlanche, Daniel) – Secondary – rechargeable cell – lead acid accumulator. IVUNIT – 3 EFFECTS OF ELECTRIC CURRENT (15 periods) Heating effect. Joule’s law – Experimental verification. Thermoelectric effects – Seebeck effect – Peltier effect – Thomson effect – Thermocouple, thermoemf, neutral and inversion temperature. Thermopile. Magnetic effect of electric current – Concept of magnetic field, Oersted’s experiment – Biot-Savart law – Magnetic field due to an infinitely long current carrying straight wire and circular coil – Tangent galvanometer – Construction and working – Bar magnet as an equivalent solenoid – magnetic field lines. Ampere’s circuital law and its application. Force on a moving charge in uniform magnetic field and electric field – cyclotron – Force on current carrying conductor in a uniform magnetic field, forces between two parallel current carrying conductors – definition of ampere. Torque experienced by a current loop in a uniform magnetic field-moving coil galvanometer – Conversion to ammeter and voltmeter – Current loop as a magnetic dipole and its magnetic dipole moment – Magnetic dipole moment of a revolving electron. UNIT – 4 ELECTROMAGNETIC INDUCTION AND ALTERNATING CURRENT (14 periods) Electromagnetic induction – Faraday’s law – induced emf and current – Lenz’s law. Self induction – Mutual induction – Self inductance of a long solenoid – mutual inductance of two long solenoids. Methods of inducing emf – (1) by changing magnetic induction (2) by changing area enclosed by the coil and (3) by changing the orientation of the coil (quantitative treatment) analytical treatment can also be included. AC generator – commercial generator. (Single phase, three phase). Eddy current – Applications – Transformer – Long distance transmission. Alternating current – measurement of AC – AC circuit with resistance – AC circuit with inductor – AC circuit with capacitor - LCR series circuit – Resonance and Q – factor: power in AC circuits. VUNIT–5 ELECTROMAGNETIC WAVES AND WAVE OPTICS (17 periods) Electromagnetic waves and their characteristics – Electromagnetic spectrum, Radio, microwaves, Infra red, visible, ultra violet – X rays, gamma rays. Emission and Absorption spectrum – Line, Band and continuous spectra – Flourescence and phosphorescence. Theories of light – Corpuscular – Wave – Electromagnetic and Quantum theories. Scattering of light – Rayleigh’s scattering – Tyndal scattering – Raman effect – Raman spectrum – Blue colour of the sky and reddish appearance of the sun at sunrise and sunset. Wavefront and Huygen’s principle – Reflection, Total internal reflection and refraction of plane wave at a plane surface using wavefronts. Interference – Young’s double slit experiment and expression for fringe width – coherent source - interference of light. Formation of colours in thin films – analytical treatment – Newton’s rings. Diffraction – differences between interference and diffraction of light – diffraction grating. Polarisation of light waves – polarisation by reflection – Brewster’s law - double refraction - nicol prism – uses of plane polarised light and polaroids – rotatory polarisation – polarimeter UNIT – 6 ATOMIC PHYSICS (16 periods) Atomic structure – discovery of the electron – specific charge (Thomson’s method) and charge of the electron (Millikan’s oil drop method) – alpha scattering – Rutherford’s atom model. Bohr’s model – energy quantisation – energy and wave number expression – Hydrogen spectrum – energy level diagrams – sodium and mercury spectra - excitation and ionization potentials. Sommerfeld’s atom model. X-rays – production, properties, detection, absorption, diffraction of X-rays – Laue’s experiment – Bragg’s law, Bragg’s X-ray spectrometer – X-ray spectra – continuous and characteristic X–ray spectrum – Mosley’s law and atomic number. Masers and Lasers – spontaneous and stimulated emission – normal population and population inversion – Ruby laser, He–Ne laser – properties and applications of laser light – holography VIUNIT – 7 DUAL NATURE OF RADIATION AND MATTER – RELATIVITY (10 periods) Photoelectric effect – Light waves and photons – Einstein’s photo – electric equation – laws of photo – electric emission – particle nature of energy – photoelectric equation – work function – photo cells and their application. Matter waves – wave mechanical concept of the atom – wave nature of particles – De–Broglie relation – De–Broglie wave length of an electron – electron microscope. Concept of space, mass, time – Frame of references. Special theory of relativity – Relativity of length, time and mass with velocity 2 – (E = mc ). UNIT – 8 NUCLEAR PHYSICS (14 periods) Nuclear properties – nuclear Radii, masses, binding energy, density, charge – isotopes, isobars and isotones – Nuclear mass defect – binding energy. Stability of nuclei-Bain bridge mass spectrometer. Nature of nuclear forces – Neutron – discovery – properties – artificial transmutation – particle accelerator Radioactivity – alpha, beta and gamma radiations and their properties, α-decay, β-decay and γ-decay – Radioactive decay law – half life – mean life. Artificial radioactivity – radio isotopes – effects and uses Geiger – Muller counter. Radio carbon dating – biological radiation hazards Nuclear fission – chain reaction – atom bomb – nuclear reactor – nuclear fusion – Hydrogen bomb – cosmic rays – elementary particles. UNIT – 9 SEMICONDUCTOR DEVICES AND THEIR APPLICATIONS (26 periods) Semiconductor theory – energy band in solids – difference between metals, insulators and semiconductors based on band theory – semiconductor doping – Intrinsic and Extrinsic semi conductors. Formation of P-N Junction – Barrier potential and depletion layer. – P-N Junction diode – Forward and reverse bias characteristics – diode as a rectifier – zener diode. Zener diode as a voltage regulator – LED. VIIJunction transistors – characteristics – transistor as a switch – transistor as an amplifier – transistor biasing – RC, LC coupled and direct coupling in amplifier – feeback amplifier – positive and negative feed back – advantages of negative feedback amplifier – oscillator – condition for oscillations – LC circuit – Colpitt oscillator. Logic gates – NOT, OR, AND, EXOR using discret components – NAND and NOR gates as universal gates – integrated circuits. Laws and theorems of Boolean’s algebra – operational amplifier – parameters – pin-out configuration – Basic applications. Inverting amplifier. Non-inverting amplifier – summing and difference amplifiers. Measuring Instruments – Cathode Ray oscillocope – Principle – Functional units – uses. Multimeter – construction and uses. UNIT – 10 COMMUNICATION SYSTEMS (15 periods) Modes of propagation, ground wave – sky wave propagation. Amplitude modulation, merits and demerits – applications – frequency modulation – advantages and applications – phase modulation. Antennas and directivity. Radio transmission and reception – AM and FM – superheterodyne receiver. T.V.transmission and reception – scanning and synchronising. Vidicon (camera tube) and picture tube – block diagram of a monochrome TV transmitter and receiver circuits. Radar – principle – applications. Digital communication – data transmission and reception – principles of fax, modem, satellite communication – wire, cable and Fibre - optical communication. VIIIEXPERIMENTS (12 × 2 = 24 periods) 1. To determine the refractive index of the material of the prism by finding angle of prism and angle of minimum deviation using a spectrometer. 2. To determine wavelengths of a composite light using a diffraction grating and a spectrometer by normal incidence method (By assuming N). 3. To determine the radius of curvature of the given convex lens using Newton’s rings experiment. 4. To find resistance of a given wire using a metre bridge and hence determine the specific resistance of the material. 5. To compare the emf’s of two primary cells using potentiometer. 6. To determine the value of the horizontal component of the magnetic induction of the earth’s magnetic field, using tangent galvanometer. 7. To determine the magnetic field at a point on the axis of a circular coil. 8. To find the frequency of the alternating current (a.c) mains using a sonometer wire. 9. (a) To draw the characteristic curve of a p-n junction diode in forward bias and to determine its forward resistance. (b) To draw the characteristic curve of a Zener diode and to determine its reverse breakdown voltage. 10. To study the characteristics of a common emitter NPN transistor and to find out its input, output impedances and current gain. 11. Construct a basic amplifier (OP amp) using IC 741 (inverting, non inverting, summing). 12. Study of basic logic gates using integrated circuits NOT, AND, OR, NAND, NOR and EX-OR gates. IXCONTENTS Page No. 1 Electrostatics 1 2 Current Electricity 53 3 Effects of Electric Current 88 4 Electromagnetic Induction and Alternating Current 134 5 Electromagnetic Waves and Wave Optics 178 Logarithmic and other tables 228 (Unit 6 to 10 continues in Volume II) X1. Electrostatics Electrostatics is the branch of Physics, which deals with static electric charges or charges at rest. In this chapter, we shall study the basic phenomena about static electric charges. The charges in a electrostatic field are analogous to masses in a gravitational field. These charges have forces acting on them and hence possess potential energy. The ideas are widely used in many branches of electricity and in the theory of atom. 1.1 Electrostatics – frictional electricity In 600 B.C., Thales, a Greek Philosopher observed that, when a piece of amber is rubbed with fur, it acquires the property of attracting th light objects like bits of paper. In the 17 century, William Gilbert discovered that, glass, ebonite etc, also exhibit this property, when rubbed with suitable materials. The substances which acquire charges on rubbing are said to be ‘electrified’ or charged. These terms are derived from the Greek word elektron, meaning amber. The electricity produced by friction is called frictional electricity. If the charges in a body do not move, then, the frictional electricity is also known as Static Electricity. 1.1.1 Two kinds of charges (i) If a glass rod is rubbed with a silk cloth, it acquires positive charge while the silk cloth acquires an equal amount of negative charge. (ii) If an ebonite rod is rubbed with fur, it becomes negatively charged, while the fur acquires equal amount of positive charge. This classification of positive and negative charges were termed by American scientist, Benjamin Franklin. Thus, charging a rod by rubbing does not create electricity, but simply transfers or redistributes the charges in a material. 1+ + +++++ 1.1.2 Like charges repel and unlike charges attract each other – experimental verification. A charged glass rod is suspended by a silk thread, such that it swings horizontally. Now another charged glass rod is brought near the end of the suspended glass rod. It is found that the ends of the two rods repel each other (Fig 1.1). However, if a charged ebonite rod is brought near the end of the suspended rod, the two rods attract each other (Fig 1.2). The above experiment shows that like charges repel and unlike charges attract each other. Silk Silk Glass F Glass F F F Glass Ebonite Fig 1.2 Two charged rods Fig. 1.1 Two charged rods of opposite sign of same sign The property of attraction and repulsion between charged bodies have many applications such as electrostatic paint spraying, powder coating, fly−ash collection in chimneys, ink−jet printing and photostat copying (Xerox) etc. 1.1.3 Conductors and Insulators According to the electrostatic behaviour, materials are divided into two categories : conductors and insulators (dielectrics). Bodies which allow the charges to pass through are called conductors. e.g. metals, human body, Earth etc. Bodies which do not allow the charges to pass through are called insulators. e.g. glass, mica, ebonite, plastic etc. 2 - - - - - - + + + + +++ +++++++ 1.1.4 Basic properties of electric charge (i) Quantisation of electric charge The fundamental unit of electric charge (e) is the charge carried by the electron and its unit is coulomb. e has the magnitude −19 1.6 × 10 C. In nature, the electric charge of any system is always an integral multiple of the least amount of charge. It means that the quantity can take only one of the discrete set of values. The charge, q = ne where n is an integer. (ii) Conservation of electric charge Electric charges can neither be created nor destroyed. According to the law of conservation of electric charge, the total charge in an isolated system always remains constant. But the charges can be transferred from one part of the system to another, such that the total 238 charge always remains conserved. For example, Uranium ( U ) can 92 4 decay by emitting an alpha particle ( He nucleus) and transforming to 2 234 thorium ( Th ). 90 238 234 4 U −−−−→ Th + He 92 90 2 Total charge before decay = +92e, total charge after decay = 90e + 2e. Hence, the total charge is conserved. i.e. it remains constant. (iii) Additive nature of charge The total electric charge of a system is equal to the algebraic sum of electric charges located in the system. For example, if two charged bodies of charges +2q, −5q are brought in contact, the total charge of the system is –3q. 1.1.5 Coulomb’s law The force between two charged bodies was studied by Coulomb in 1785. Coulomb’s law states that the force of attraction or repulsion between two point charges is directly proportional to the product of the charges and inversely proportional to the square of the distance between 3q q 2 1 them. The direction of forces is along F F the line joining the two point charges. r Let q and q be two point charges 1 2 Fig 1.3a Coulomb forces placed in air or vacuum at a distance r apart (Fig. 1.3a). Then, according to Coulomb’s law, qq qq 12 12 F α or F = k 2 2 r r where k is a constant of proportionality. In air or vacuum, 1 k = , where ε is the permittivity of free space (i.e., vacuum) and o 4πε o −12 2 −1 −2 the value of ε is 8.854 × 10 C N m . o 1 qq 12 F = …(1) 2 4πε r o 1 9 2 −2 and = 9 × 10 N m C 4πε o In the above equation, if q = q = 1C and r = 1m then, 1 2 11 × 9 9 F = (9 × 10 ) = 9 × 10 N 2 1 One Coulomb is defined as the quantity of charge, which when placed at a distance of 1 metre in air or vacuum from an equal and 9 similar charge, experiences a repulsive force of 9 × 10 N. If the charges are situated in a medium of permittivity ε, then the magnitude of the force between them will be, qq 1 12 F = …(2) 2 m 4πε r Dividing equation (1) by (2) F ε == ε r F ε m ο 4ε The ratio = ε , is called the relative permittivity or dielectric r ε ο constant of the medium. The value of ε for air or vacuum is 1. r ∴ ε = ε ε o r F Since F = , the force between two point charges depends on m ε r the nature of the medium in which the two charges are situated. Coulomb’s law – vector form q q 2 1 r → 12 If F is the force exerted on charge 21 ++ r F F 12 21 q by charge q (Fig.1.3b), 2 1 → qq 12 F r q = k q 2 21 12 1 2 r 12 r + 12 F F 12 21 where r is the unit vector 12 r from q to q . 1 2 Fig 1.3b Coulomb’s law in → If F is the force exerted on 12 vector form q due to q , 1 2 qq 12 → k F = r 2 12 21 r 21 where r is the unit vector from q to q . 21 2 1 Both r and r have the same magnitude, and are oppositely 21 12 directed qq 12 → = k ∴ F 2 (– r ) 12 12 r 12 qq 12 → =− k or F 2 r 12 12 r 12 → → or F = – F 12 21 So, the forces exerted by charges on each other are equal in magnitude and opposite in direction. 51.1.6 Principle of Superposition The principle of superposition is to calculate the electric force experienced by a charge q due to other charges q , q ……. q . 1 2 3 n The total force on a given charge is the vector sum of the forces exerted on it due to all other charges. The force on q due to q 1 2 1 qq 12 → = F r 2 12 4πε 21 r ο 21 Similarly, force on q due to q 1 3 1 qq 13 → = F r 2 13 4πε 31 r ο 31 The total force F on the charge q by all other charges is, 1 1 → → → → → F = F + F + F F 1 12 13 14 ......... + 1n Therefore, qq qq q q 1⎡⎤ 12 13 1 n → ˆˆ ˆ rr++ ....... r = 21 31 n1 F⎢⎥ 22 2 1 rr r 4πε ο⎣⎦ 21 31 n1 1.2 Electric Field Electric field due to a charge is the space around the test charge in which it experiences a force. The presence of an electric field around a charge cannot be detected unless another charge is brought towards it. When a test charge q is placed near a charge q, which is the o source of electric field, an electrostatic force F will act on the test charge. Electric Field Intensity (E) Electric field at a point is measured in terms of electric field intensity. Electric field intensity at a point, in an electric field is defined as the force experienced by a unit positive charge kept at that point. 6F = E It is a vector quantity. . The unit of electric field intensity q o −1 is N C . The electric field intensity is also referred as electric field strength or simply electric field. So, the force exerted by an electric field on a charge is F = q E. o 1.2.1 Electric field due to a point charge Let q be the point charge +q +q 0 placed at O in air (Fig.1.4). A test E r O P charge q is placed at P at a o distance r from q. According to Fig 1.4 Electric field due to a Coulomb’s law, the force acting on point charge q due to q is o 1 qq o F = 2 4πε r o The electric field at a point P is, by definition, the force per unit test charge. Fq 1 = E = 2 q 4πε r oo The direction of E is along the line joining O and P, pointing away from q, if q is positive and towards q, if q is negative. → 1 q = In vector notation E r, where r is a unit vector pointing 2 4πε r o away from q. 1.2.2 Electric field due to system of charges If there are a number of stationary charges, the net electric field (intensity) at a point is the vector sum of the individual electric fields due to each charge. → → → → → E = E + E + E ...... E 1 2 3 n q q q 1⎡⎤ 1 2 3 rr ++ r +......... = 12 3 ⎢⎥ 22 2 rr r 4πε o⎣⎦ 12 3 7 1.2.3 Electric lines of force The concept of field lines was introduced by Michael Faraday as an aid in visualizing electric and magnetic fields. Electric line of force is an imaginary straight or curved path along which a unit positive charge tends to move in an electric field. The electric field due to simple arrangements of point charges are shown in Fig 1.5. +q +q -q +q +q (a) (b) (c) Isolated charge Unlike charges Like charges Fig1.5 Lines of Forces Properties of lines of forces: (i) Lines of force start from positive charge and terminate at negative charge. (ii) Lines of force never intersect. (iii) The tangent to a line of force at any point gives the direction of the electric field (E) at that point. (iv) The number of lines per unit area, through a plane at right angles to the lines, is proportional to the magnitude of E. This means that, where the lines of force are close together, E is large and where they are far apart, E is small. 1 (v) Each unit positive charge gives rise to lines of force in free ε o space. Hence number of lines of force originating from a point q charge q is N = in free space. ε o 81.2.4 Electric dipole and electric dipole moment Two equal and opposite charges separated by a very small distance p -q +q constitute an electric dipole. 2d Water, ammonia, carbon−dioxide and Fig 1.6 Electric dipole chloroform molecules are some examples of permanent electric dipoles. These molecules behave like electric dipole, because the centres of positive and negative charge do not coincide and are separated by a small distance. Two point charges +q and –q are kept at a distance 2d apart (Fig.1.6). The magnitude of the dipole moment is given by the product of the magnitude of the one of the charges and the distance between them. ∴ Electric dipole moment, p = q2d or 2qd. It is a vector quantity and acts from –q to +q. The unit of dipole moment is Cm. 1.2.5 Electric field due to an electric dipole at a point on its axial line. AB is an electric dipole of two point charges –q and +q separated by a small distance 2d (Fig 1.7). P is a point along the axial line of the dipole at a distance r from the midpoint O of the electric dipole. E E 2 1 AB O P -q x axis +q 2d r Fig 1.7 Electric field at a point on the axial line The electric field at the point P due to +q placed at B is, 1 q E = (along BP) 2 1 4πε () rd − o 9The electric field at the point P due to –q placed at A is, 1 q E = (along PA) 2 2 4πε () rd + o E and E act in opposite directions. 1 2 Therefore, the magnitude of resultant electric field (E) acts in the direction of the vector with a greater magnitude. The resultant electric field at P is, E = E + (−E ) 1 2 11qq ⎡⎤ − E = ⎢⎥ along BP. 22 44 πε πε () rd−+(r d) oo ⎣⎦ 11 ⎡⎤ q − E = ⎢⎥ along BP 22 4πε () rd−+(r d) o⎣⎦ ⎡⎤ 4rd q E = ⎢⎥along BP. 222 4πε() rd − o⎣⎦ If the point P is far away from the dipole, then d r qr44 d q d = ∴ E = 43 44 πε πε rr oo 12p E = along BP. 3 4πε r o Electric dipole moment p = q x 2d ∵ E acts in the direction of dipole moment. 10