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      Class 12 PHYSICS – JEE

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      • Class 12 PHYSICS – JEE
      CoursesClass 12PhysicsClass 12 PHYSICS – JEE
      • 1.Electrostatics (1)
        8
        • Lecture1.1
          Charge, Coulombs Law and Coulombs law in Vector form 41 min
        • Lecture1.2
          Electric Field; Electric Field Lines; Field lines due to multiple charges 42 min
        • Lecture1.3
          Charge Distribution; Finding Electric Field due to Different Object 01 hour
        • Lecture1.4
          Solid angle; Area Vector; Electric Flux; Flux of closed surface; Gauss Law 47 min
        • Lecture1.5
          Finding E Using Concept of Gauss law and Flux 01 hour
        • Lecture1.6
          Chapter Notes – Electrostatics (1)
        • Lecture1.7
          NCERT Solutions – Electrostatics
        • Lecture1.8
          Revision Notes Electrostatics
      • 2.Electrostatics (2)
        7
        • Lecture2.1
          Work done by Electrostatic Force; Work done by man in E-Field; Electrostatic Potential Energy 49 min
        • Lecture2.2
          Finding Electric Potential, Equipotential Surface and Motion in Electric Field 01 hour
        • Lecture2.3
          Electric Dipole and Dipole in Uniform and Non-uniform Electric field 01 hour
        • Lecture2.4
          Analysis of charge on conductors; Potential due to induced charge 58 min
        • Lecture2.5
          Conductors with cavity- Case 1: Empty cavity, Case 2: Charge Inside Cavity 41 min
        • Lecture2.6
          Connecting Two Conductors; Grounding of conductor; Electric field just outside conductor; Electrostatic pressure; Self potential Energy 54 min
        • Lecture2.7
          Chapter Notes – Electrostatics (2)
      • 3.Current Electricity (1)
        9
        • Lecture3.1
          Current, Motion of Electrons in Conductor; Temp. Dependence of Resistor 26 min
        • Lecture3.2
          Circuit Theory and Kirchoffs Laws 31 min
        • Lecture3.3
          Some Special Circuits- Series & Parallel Circuits, Open Circuit, Short Circuit 26 min
        • Lecture3.4
          Wheatstone Bridge, Current Antisymmetric 21 min
        • Lecture3.5
          Equivalent Resistance- Series and parallel, Equipotential Points, Wheatstone Bridge 25 min
        • Lecture3.6
          Current Antisymmetric, Infinite Ladder, Circuit Solving, 3D circuits 20 min
        • Lecture3.7
          Chapter Notes – Current Electricity
        • Lecture3.8
          NCERT Solutions – Current Electricity
        • Lecture3.9
          Revision Notes Current Electricity
      • 4.Current Electricity (2)
        4
        • Lecture4.1
          Heating Effect of Current; Rating of Bulb; Fuse 19 min
        • Lecture4.2
          Battery, Maximum power theorem; Ohmic and Non Ohmic Resistance; Superconductor 31 min
        • Lecture4.3
          Galvanometer; Ammeter & Voltmeter and Their Making 44 min
        • Lecture4.4
          Potentiometer and its applications ; Meter Bridge; Post Office Box; Colour Code of Resistors 32 min
      • 5.Capacitor
        6
        • Lecture5.1
          Capacitor and Capacitance; Energy in Capacitor 38 min
        • Lecture5.2
          Capacitive Circuits- Kirchoff’s Laws; Heat Production 01 hour
        • Lecture5.3
          Equivalent Capacitance; Charge on both sides of cap. Plate 52 min
        • Lecture5.4
          Dielectric Strength; Polar and Non-Polar Dielectric; Equivalent Cap. with Dielectric 01 hour
        • Lecture5.5
          Inserting and Removing Dielectric- Work (Fringing Effect), Force; Force between plates of capacitor 38 min
        • Lecture5.6
          Revision Notes Capacitor
      • 6.RC Circuits
        3
        • Lecture6.1
          Maths Needed for RC Circuits, RC circuits-Charging Circuit 19 min
        • Lecture6.2
          RC circuits-Discharging Circuit, Initial & Steady State, Final (Steady) State, Internal Resistance of Capacitor 44 min
        • Lecture6.3
          Revision Notes RC Circuits
      • 7.Magnetism and Moving Charge
        16
        • Lecture7.1
          Introduction, Vector Product, Force Applied by Magnetic Field, Lorentz Force, Velocity Selector 40 min
        • Lecture7.2
          Motion of Charged Particles in Uniform Magnetic Field 40 min
        • Lecture7.3
          Cases of Motion of Charged Particles in Uniform Magnetic Field 56 min
        • Lecture7.4
          Force on a Current Carrying Wire on Uniform B and its Cases, Questions and Solutions 59 min
        • Lecture7.5
          Magnetic Field on Axis of Circular Loop, Magnetic field due to Moving Charge, Magnetic Field due to Current 52 min
        • Lecture7.6
          Magnetic Field due to Straight Wire, Different Methods 40 min
        • Lecture7.7
          Magnetic Field due to Rotating Ring and Spiral 41 min
        • Lecture7.8
          Force between Two Current Carrying Wires 36 min
        • Lecture7.9
          Force between Two Current Carrying Wires 58 min
        • Lecture7.10
          Miscellaneous Questions 55 min
        • Lecture7.11
          Solenoid, Toroid, Magnetic Dipole, Magnetic Dipole Momentum, Magnetic Field of Dipole 54 min
        • Lecture7.12
          Magnetic Dipole in Uniform Magnetic Field, Moving Coil Galvanometer, Torsional Pendulum 01 hour
        • Lecture7.13
          Advanced Questions, Magnetic Dipole and Angular Momentum 56 min
        • Lecture7.14
          Chapter Notes – Magnetism and Moving Charge
        • Lecture7.15
          NCERT Solutions – Magnetism and Moving Charge
        • Lecture7.16
          Revision Notes Magnetism and Moving Charge
      • 8.Magnetism and Matter
        10
        • Lecture8.1
          Magnetic Dipole, Magnetic Properties of Matter, Diamagnetism; Domain Theory of Ferro 47 min
        • Lecture8.2
          Magnetic Properties of Matter in Detail 39 min
        • Lecture8.3
          Magnetization and Magnetic Intensity, Meissner Effect, Variation of Magnetization with Temperature 55 min
        • Lecture8.4
          Hysteresis, Permanent Magnet, Properties of Ferro for Permanent Magnet, Electromagnet 31 min
        • Lecture8.5
          Magnetic Compass, Earth’s Magnetic Field 20 min
        • Lecture8.6
          Bar Magnet, Bar Magnet in Uniform Field 49 min
        • Lecture8.7
          Magnetic Poles, Magnetic Field Lines, Magnetism and Gauss’s Law 32 min
        • Lecture8.8
          Chapter Notes – Magnetism and Matter
        • Lecture8.9
          NCERT Solutions – Magnetism and Matter
        • Lecture8.10
          Revision Notes Magnetism and Matter
      • 9.Electromagnetic Induction
        14
        • Lecture9.1
          Introduction, Magnetic Flux, Motional EMF 01 min
        • Lecture9.2
          Induced Electric Field, Faraday’s Law, Comparison between Electrostatic Electric Field and Induced Electric Field 43 min
        • Lecture9.3
          Induced Current; Faraday’s Law ; Lenz’s Law 56 min
        • Lecture9.4
          Faraday’s Law and its Cases 50 min
        • Lecture9.5
          Advanced Questions on Faraday’s Law 37 min
        • Lecture9.6
          Cases of Current Electricity 59 min
        • Lecture9.7
          Lenz’s Law and Conservation of Energy, Eddy Current, AC Generator, Motor 01 hour
        • Lecture9.8
          Mutual Induction 53 min
        • Lecture9.9
          Self Inductance, Energy in an Inductor 34 min
        • Lecture9.10
          LR Circuit, Decay Circuit 01 hour
        • Lecture9.11
          Initial and Final Analysis of LR Circuit 38 min
        • Lecture9.12
          Chapter Notes – Electromagnetic Induction
        • Lecture9.13
          NCERT Solutions – Electromagnetic Induction
        • Lecture9.14
          Revision Notes Electromagnetic Induction
      • 10.Alternating Current Circuit
        8
        • Lecture10.1
          Introduction, AC/DC Sources, Basic AC Circuits, Average & RMS Value 46 min
        • Lecture10.2
          Phasor Method, Rotating Vector, Adding Phasors, RC Circuit 35 min
        • Lecture10.3
          Examples and Solutions 21 min
        • Lecture10.4
          Power in AC Circuit, Resonance Frequency, Bandwidth and Quality Factor, Transformer 51 min
        • Lecture10.5
          LC Oscillator, Question and Solutions of LC Oscillator, Damped LC Oscillator 53 min
        • Lecture10.6
          Chapter Notes – Alternating Current Circuit
        • Lecture10.7
          NCERT Solutions – Alternating Current Circuit
        • Lecture10.8
          Revision Notes Alternating Current Circuit
      • 11.Electromagnetic Waves
        4
        • Lecture11.1
          Displacement Current; Ampere Maxwell Law 14 min
        • Lecture11.2
          EM Waves; EM Spectrum; Green House Effect; Ozone Layer 36 min
        • Lecture11.3
          Chapter Notes – Electromagnetic Waves
        • Lecture11.4
          Revision Notes Electromagnetic Waves
      • 12.Photoelectric Effect
        5
        • Lecture12.1
          Recalling Basics; Photoelectric Effect 50 min
        • Lecture12.2
          Photo-electric Cell 35 min
        • Lecture12.3
          Photon Flux; Photon Density; Momentum of Photon; Radiation Pressure- Full Absorption, Full Reflection; Dual nature 52 min
        • Lecture12.4
          Chapter Notes – Photoelectric Effect
        • Lecture12.5
          Revision Notes Photoelectric Effect
      • 13.Ray Optics (Part 1)
        12
        • Lecture13.1
          Rays and Beam of Light, Reflection of Light, Angle of Deviation, Image Formation by Plane Mirror 01 hour
        • Lecture13.2
          Field of View, Numerical on Field of Line, Size of Mirror 42 min
        • Lecture13.3
          Curved Mirrors, Terms Related to Curved Mirror, Reflection of Light by Curved Mirror 40 min
        • Lecture13.4
          Image Formation by Concave Mirror, Magnification or Lateral or Transverse Magnification 01 hour
        • Lecture13.5
          Ray Diagrams for Concave Mirror 45 min
        • Lecture13.6
          Image Formation by Convex Mirror; Derivations of Various Formulae used in Concave Mirror and Convex Mirror 01 hour
        • Lecture13.7
          Advanced Optical Systems, Formation of Images with more than one Mirror 24 min
        • Lecture13.8
          Concept of Virtual Object, Formation of Image when Incident ray are Converging, Image Characteristics for Virtual Object, 55 min
        • Lecture13.9
          Newton’s Formula, Longitudinal Magnification 23 min
        • Lecture13.10
          Formation of Image when Two Plane Mirrors kept at an angle and parallel; Formation of Image by two Parallel Mirrors. 43 min
        • Lecture13.11
          Chapter Notes – Ray Optics
        • Lecture13.12
          NCERT Solutions – Ray Optics
      • 14.Ray Optics (Part 2)
        13
        • Lecture14.1
          Refractive Index, Opaque, Transparent, Speed of Light, Relative Refractive Index, Refraction and Snell’s Law, Refraction in Denser and Rarer Medium 42 min
        • Lecture14.2
          Image Formation due to Refraction; Derivation; Refraction and Image formation in Glass Slab 57 min
        • Lecture14.3
          Total Internal Reflection, Critical Angle, Principle of Reversibility 01 hour
        • Lecture14.4
          Application of Total Internal Reflection 45 min
        • Lecture14.5
          Refraction at Curved Surface, Image Formation by Curved Surface, Derivation 56 min
        • Lecture14.6
          Image Formation by Curved Surface, Snell’s Law in Vector Form 01 hour
        • Lecture14.7
          Lens, Various types of Lens, Differentiating between various Lenses; Optical Centre, Derivation of Lens Maker Formula 01 hour
        • Lecture14.8
          Lens Formula, Questions and Answers 39 min
        • Lecture14.9
          Property of Image by Convex and Concave Lens; Lens Location, Minimum Distance Between Real Image and Object 01 hour
        • Lecture14.10
          Power of Lens, Combination of Lens, Autocollimation 35 min
        • Lecture14.11
          Silvering of Lens 44 min
        • Lecture14.12
          Cutting of Lens and Mirror, Vertical Cutting, Horizontal Cutting 49 min
        • Lecture14.13
          Newton’s Law for Lens and Virtual Object 01 hour
      • 15.Ray Optics (Part 3)
        6
        • Lecture15.1
          Prism, Angle of Prism, Reversibility in Prism 51 min
        • Lecture15.2
          Deviation in Prism, Minimum and Maximum Deviation, Asymmetric, Thin Prism, Proof for formula of Thin Prism 59 min
        • Lecture15.3
          Dispersion of Light, Refractive Index, Composition of Light, Dispersion through Prism 01 hour
        • Lecture15.4
          Rainbow Formation, Scattering of Light, Tyndall Effect, Defects of Image, Spherical Defect, Chromatic Defect, Achromatism. 57 min
        • Lecture15.5
          Optical Instruments, The Human Eye, Defects of Eye and its Corrections 01 hour
        • Lecture15.6
          Microscope & Telescope 02 hour
      • 16.Wave Optics
        21
        • Lecture16.1
          Introduction to Wave Optics 11 min
        • Lecture16.2
          Huygens Wave Theory 14 min
        • Lecture16.3
          Huygens Theory of Secondary Wavelets 10 min
        • Lecture16.4
          Law of Reflection by Huygens Theory 10 min
        • Lecture16.5
          Deriving Laws of Refraction by Huygens Wave Theory 10 min
        • Lecture16.6
          Multiple Answer type question on Huygens Theory 41 min
        • Lecture16.7
          Conditions of Constructive and Destructive Interference 22 min
        • Lecture16.8
          Conditions of Constructive and Destructive Interference 06 min
        • Lecture16.9
          Conditions of Constructive and Destructive Interference 23 min
        • Lecture16.10
          Incoherent Sources of Light 38 min
        • Lecture16.11
          Youngs Double Slit Experiment 12 min
        • Lecture16.12
          Fringe Width Positions of Bright and Dark Fringes 15 min
        • Lecture16.13
          Numerical problems on Youngs Double Slit Experiment 11 min
        • Lecture16.14
          Numerical problems on Youngs Double Slit Experiment 19 min
        • Lecture16.15
          Displacement of Interference Pattern 19 min
        • Lecture16.16
          Numerical problems on Displacement of Interference Pattern 28 min
        • Lecture16.17
          Shapes of Fringes 37 min
        • Lecture16.18
          Colour of Thin Films 59 min
        • Lecture16.19
          Interference with White Light 32 min
        • Lecture16.20
          Chapter Notes – Wave Optics
        • Lecture16.21
          NCERT Solutions – Wave Optics
      • 17.Atomic Structure
        6
        • Lecture17.1
          Thomson and Rutherford Model of Atom; Trajectory of Alpha particle; Bohr’s Model ; Hydrogen Like Atom; Energy Levels 58 min
        • Lecture17.2
          Emission Spectra, Absorption Spectra; De Broglie Explanation of Bohr’s 2nd Postulate; Limitations of Bohr’s Model 37 min
        • Lecture17.3
          Momentum Conservation in Photon Emission, Motion of Nucleus, Atomic Collision 58 min
        • Lecture17.4
          Chapter Notes – Atomic Structure
        • Lecture17.5
          NCERT Solutions – Atomic Structure
        • Lecture17.6
          Revision Notes Atomic Structure
      • 18.Nucleus
        6
        • Lecture18.1
          Basics- Size of Nucleus, Nuclear Force, Binding Energy, Mass Defect; Radioactive Decay 01 hour
        • Lecture18.2
          Laws of Radioactive Decay 36 min
        • Lecture18.3
          Nuclear Fission; Nuclear Reactor; Nuclear Fusion- Reaction Inside Sun 30 min
        • Lecture18.4
          Chapter Notes – Nucleus
        • Lecture18.5
          NCERT Solutions – Nucleus
        • Lecture18.6
          Revision Notes Nucleus
      • 19.X-Ray
        4
        • Lecture19.1
          Electromagnetic Spectrum, Thermionic Emission; Coolidge Tube – Process 1 22 min
        • Lecture19.2
          Coolidge Tube – Process 2; Moseley’s Law; Absorption of X-rays in Heavy Metal 39 min
        • Lecture19.3
          Chapter Notes – X-Ray
        • Lecture19.4
          Revision Notes X-Ray
      • 20.Error and Measurement
        2
        • Lecture20.1
          Least Count of Instruments; Mathematical Operation on Data with Random Error 18 min
        • Lecture20.2
          Significant Digits; Significant Digits and Mathematical Operations 30 min
      • 21.Semiconductors
        9
        • Lecture21.1
          Conductor, Semiconductors and Insulators Basics Difference, Energy Band Theory, Si element 21 min
        • Lecture21.2
          Doping and PN Junction 01 hour
        • Lecture21.3
          Diode and Diode as Rectifier 01 hour
        • Lecture21.4
          Voltage Regulator and Zener Diode and Optoelectronic Jn. Devices 01 hour
        • Lecture21.5
          Transistor, pnp, npn, Modes of operation, Input and Output Characteristics, , Current Amplification Factor 01 hour
        • Lecture21.6
          Transistor as Amplifier, Transistor as Switch, Transistor as Oscillator, Digital Gates 01 hour
        • Lecture21.7
          Chapter Notes – Semiconductors
        • Lecture21.8
          NCERT Solutions – Semiconductors
        • Lecture21.9
          Revision Notes Semiconductors
      • 22.Communication Systems
        5
        • Lecture22.1
          Basic working and terms; Antenna; Modulation and Types of Modulation 32 min
        • Lecture22.2
          Amplification Modulation, Transmitter, Receiver, Modulation index 40 min
        • Lecture22.3
          Chapter Notes – Communication Systems
        • Lecture22.4
          NCERT Solutions – Communication Systems
        • Lecture22.5
          Revision Notes Communication Systems

        Chapter Notes – Electromagnetic Waves

        Light may be described as a wave. The wave equation for light propagating in x-direction in vacuum may be written as

        E=Eosinω(t−x/c)

        where E is the sinusoidally varying electric field at position x at time t. The constant c is the speed of light in vacuum.
        There is also a sinusoidally varying magnetic field associated with electric field when light propagates. The magnetic field is perpendicular to the direction of propagation as well as to the electric field E. It is given by

        B=Bosinω(t−x/c)

        Such a combination of mutually perpendicular electric and magnetic fields is referred to as an electromagnetic wave in vacuum.

        MAXWELL’S DISPLACEMENT CURRENT

        Maxwell discovered the concept of displacement current. Displacement current is that which results due to the displacement of electrons. The displacement of electrons is caused by the time varying electric field. The generalized form of Ampere’s law ∮B.dl=μoI, which includes both conduction current IC (current flowing through the conducting wire) and displacement current IC as given by Maxwell i.e.

        ∮B.dl=μo(IC+ID)

        where IC=dqdt ,  where dqdt is rate of flow of charge.
        and ID=εodΦEdt
        Here  ΦE   is electric flux.
        Therefore modified Ampere’s law may be expressed as

        ∫B⃗ .dl⃗ =μo(IC+εodΦEdt)

        Example 1
        Figure shows a capacitor made of two circular plates each of radius 12 cm and separated by 5.0 mm. The capacitor is being charged by an external source (not shown in the figure). The charging current is constant and is equal to 0.15 A.
        (a) Calculate the capacitance and the rate of change of potential difference between the plates.
        (b)  Obtain the displacement current across the plates.
        (c)  Is Kirchhoff’s first rule valid at each plate of the capacitor? Explain.
        Given that ε0=8.85×10−12C2N−1m−2.

        Solution:

        Here,   d = 5.0 mm = 5.0 x 10-3 m; R = 12 cm = 12 x 10-2 m, I = 0.15 A.
        ε0=8.85×10−12C2N−1m−2
        Now,   A = πR2 = π(12 x 10-2)2 = 1.44 π x 10-2 m2
        (a) The capacitance of parallel plate capacitor is given by

        C=εoAd=8.85×10−12×1.44π×10−25×10−3=80.1×10−12V

        Now, q=CV
        Therefore,  dqdt=CdVdt   or   I=CdVdt
        or   dVdt=1C=0.1580.1×10−12=1.873×109Vs−1

        (b) Displacement current is equal to conduction current i.e. 0.15 A.
        (c) Yes, Kirchhoff’s law will be valid at each plate of the capacitor, provided electric current means the sum of the conduction and displacement currents.

        Maxwell’s Equations

        The four basic laws of electricity and magnetism i.e. Gauss’s law in electrostatics, Gauss’s law in magnetism, Faraday’s law of electromagnetic induction and Maxwell-Ampere’s circuital law are called Maxwell’s equations.

        1. Gauss’s Law in Electrostatics

        ∮E⃗ .ds⃗ =q/εo

         2. Gauss’s Law in Magnetism

        ∮B⃗ .ds⃗ =0

        3. Faraday’s Law of Electromagnetic Induction

                         ε=−dΦBdt  or  ∮E⃗ .dl⃗ =−dΦBdt

        4. Maxwell-Ampere’s circuital Law               

        ∮B⃗ .dl⃗ =μo(IC+εodΦEdt)

        Nature of Electromagnetic Waves

        Maxwell’s concept of displacement current led to the conclusion that an electric field varying with time at a point produces magnetic field at that point. This symmetry in the law of electricity and magnetism leads to the conclusion that a time varying electric field gives rise to a time varying magnetic field and vice versa. Electric and magnetic fields in electromagnetic wave is of transverse nature.

        At any instant, the electric and magnetic fields varying sinusoidally with x can be expressed by equation
        Ey=Eosin(x−ct)              (1)
        and   BZ=Bosin(x−ct)     (2)
        Here Eo and Bo are the amplitudes of electric and magnetic fields along y-axis and z-axis respectively.
        Faraday’s law of electromagnetic induction states that

        ∮E⃗ .dl⃗ =−dΦBdt    (3)

        From equation (3) it can be proved that for a plane electromagnetic wave propagating along x-axis,

        ∂Ey∂x=−∂Bz∂t     (4)

        i.e. a magnetic field varying with time gives rise to an electric field varying in space.
        From equation (1), we have

        ∂Ey∂x=Eocos(x−ct)

        and from equation (2), we have

        ∂By∂t=−cBocos(x−ct)

        Substituting for ∂Ey∂x  and ∂Bz∂t  in equation (1)

        Eo=cBo     or     c=EoBo

        It shows that the velocity of electromagnetic waves is equal to the ratio of amplitudes of electric and magnetic fields.
        Velocity of electromagnetic waves is also given by

        c=1μoεo√

        Example 2
        Green light of mercury has a wavelength 5.5 x 10-5 cm.
        (a)  What is the frequency in MHz and period in μs in vacuum?
        (b)  What is the wavelength in glass, if refractive index of glass is 1.5?
        Given c = 3 x 108 m/s.

        Solution:

        Here, wavelength λ = 5.5 x 10-5 cm = 5.5 x 10-7 m
        Velocity of light, c = 3 x 108 m/s
        (a)  If ν is the frequency, then

        ν=cλ=3×1085.5×10−7 Hz = 3×1085.5×10−7×106=5.45×108 MHz

        Time period,

        T=1μ=λc=5.5×10−73×108=1.8×10−15×106=1.8×10−19μs

        (b) Now, refractive index μ=veloictyoflightinvacuumvelocityoflightinglass=cν
        Therefore, velocity of light in glass ν=cμ=3×1081.5=2×108m/s
        The wavelength of light in glass, λ=vν=vt
        =2×108×1.8×10−15=3.6×10−7m

        Energy Density of Electromagnetic Waves

        (a)  The average energy density of electric field is

        uE=12εoE2=12εo(Eo/2–√)2=14εoE2o

        (b)  The average energy density of magnetic field is,

        uB=B22μo=(Bo/2√)22μo=B2o4μo

        (c) uE=uB
        (d) Total average energy density

        uE+uB=2uE=2uB=12εoE2o=12B2oμo

        The units of uE and uB are J m-3.

        Intensity of Electromagnetic Wave

        The energy of electromagnetic wave crossing per unit time per unit area perpendicular to the direction of propagation of wave is called the intensity of electromagnetic wave.
        The intensity of electromagnetic wave is

        I=Pav4πr2=uav×c=12εoE2oc=12μoB2oc=12μo.E2oc

        Momentum of Electromagnetic Wave

        The electromagnetic wave during its propagation has linear momentum with it. The linear momentum carried by the portion of wave having energy U is given by

        p=U/c

        If the electromagnetic wave incident on a material surface is completely absorbed, it will deliver energy U and momentum p=U/c to the surface.
        If the incident wave is totally reflected from the surface, the momentum delivered to the surface =U/c−(−U/c)=2U/c. Due to which the electromagnetic waves incident on a surface exert a force on the surface.

        Radiant flux of electromagnetic wave

        According to Maxwell, the accelerated charged particles produce electromagnetic waves. The total radiant flux emitted at any instant is given by
        P=q2a2/(6πε0c3), where q is the charge on the particle and a is its instantaneous acceleration.

        Poynting Vector

        When an electromagnetic wave advances, the electromagnetic energy flows in the direction of E⃗ ×B⃗ . The total energy flowing perpendicularly per second per unit area into the surface in free space is called a Poynting vector S⃗ , where S⃗ =c2εo(E⃗ ×B⃗ )=(E⃗ ×B⃗ )/μo.
        The S. I. unit of S is watt/(metre)2.

        Radiant Flux Density

        The average value of pointing vector (S⃗ ) over a convenient time interval in the propagation of electromagnetic wave is known as radiant flux density. When energy of electromagnetic wave is incident on a surface, the flux density is called intensity of wave (denoted by I). Thus I=S
        A harmonic electromagnetic wave traveling along X-axis in free space can be described by periodic variation of electric and magnetic field along y-axis and z-axis with the equations

        E⃗ =E⃗ ocos(kx−ωt)      and     B⃗ =B⃗ ocos(kx−ωt)

        Then radiant flux density S⃗  is given by

        S⃗ =c2εo(E⃗ ×B⃗ )=c2εoE⃗ o×B⃗ ocos2(kx−ωt)

        Hence |S⃗ |=c2εo|E⃗ o×B⃗ o|cos2(kx−ωt).
        The average value of S⃗  over a single period T is given by

        S=I=c2εo|E⃗ o×B⃗ o|1T∫0Tcos2(kx−ωt)dt
        = c2εoEoBosin90o[12]                     [since 1T∫0Tcos2(kx−ωt)dt=12 ]
        = c2εoEo(Eoc)(12)=12cεoE2o=12cμoE2o

        PROPERTIES OF EM WAVES

        (i)   The direction of variation of electric field E and magnetic field B are perpendicular to each other as well as to the direction of propagation.
        (ii)  Speed of EM wave is 3 x 108 m/s in space, in any other medium it depends on the electric and magnetic properties of the medium and is independent of the amplitude of field variation.
        (iii) The electric and magnetic field variation are in phase.
        (iv) EM waves are produced by accelerating charged particle. An oscillating charge in an LC circuit also produces EM waves. These waves required no medium for its propagation.

        EM WAVE SPECTRUM

        The whole spectrum of electromagnetic spectrum and the modern terminology used for various sections of the spectrum are shown in table. Various regions do not have sharply defined boundaries.

        Various layers of our atmosphere

        Various layers in which the atmosphere has been divided are shown in figure. The actual boundaries are not sharp and the distances are approximate.
        Ozon layer: The upper region of stratosphere is rich in ozone and is called ozone layer. The ozone layer absorbs ultraviolet radiation from the sun and prevents them from reaching the earth’s surface, otherwise these can cause damage to life.

        Green house effect

        The phenomenon of heating of earth’s atmosphere due to trapping of infra-red rays, which are radiated from earth’s surface, by carbon dioxide layer in the atmosphere is called green house effect.

        Modulation and demodulation

        The process by which an audio signal is superimposed over the carrier waves is known as modulation. The modulated signal is sent through transmitting antenna.

        On the receiving end the audio signal is filtered from the carrier waves and this process is known as demodulation.

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