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Electromagnetic Waves Class 12 Notes Physics

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CBSE Class 12 Physics Chapter 8 Electromagnetic Waves notes in PDF are available for free download in myCBSEguide mobile app. The best app for CBSE students now provides Electromagnetic Waves class 12 Notes latest chapter wise notes for quick preparation of CBSE board exams and school-based annual examinations. Class 12 Physics notes on chapter 8 Electromagnetic Waves are also available for download in CBSE Guide website.

CBSE Guide Electromagnetic Waves class 12 Notes

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Class 12 Physics notes Chapter 8 Electromagnetic Waves

Download CBSE class 12th revision notes for chapter 8 Electromagnetic Waves in PDF format for free. Download revision notes for Electromagnetic Waves class 12 Notes and score high in exams. These are the Electromagnetic Waves class 12 Notes prepared by team of expert teachers. The revision notes help you revise the whole chapter 8 in minutes. Revision notes in exam days is one of the best tips recommended by teachers during exam days.

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CBSE Class 12 Physics Revision Notes Chapter 8 Electromagnetic Waves

  • Displacement Current: It is due to time-varying electric field – 
    Displacement current acts as a source of magnetic field in exactly the same way as conduction current.
  • Maxwell’s equations:
  1. Gauss law of electrostatics- Electromagnetic Waves Class 12 Notes Physics
  2. Gauss law of magnetism- Electromagnetic Waves Class 12 Notes Physics
  3. Faraday’s law of eletromagnetic induction- Electromagnetic Waves Class 12 Notes Physics
  4. Modified form of Ampere’s circuital law- Electromagnetic Waves Class 12 Notes Physics
  • Electromagnetic Waves: These waves propagates through spaceas coupled electric and magnetic fields, oscillating perpendicular to each other and to the direction of propagation of the wave.
    Electromagnetic Waves Class 12 Notes Physics
  1. Electromagnetic waves are produced only by charges that are accelerating, since acceleration is absolute, and not a relative phenomenon.
  2. An electric charge oscillating harmonically with frequency , produces electromagnetic waves of the same frequency .
  3. An electric dipole is a basic source of electromagnetic waves.
  4. Electromagnetic waves with wavelength of the order of a few metres were first produced and detected in the laboratory by Hertz in 1887. He thus verified a basic prediction of Maxwell’s equations.
  5. Electromagnetic waves are transverse in nature.
  6. They do not require any material medium for their propagation.
  • Oscillation of Electric and Magnetic Fields: These oscillate sinusoidally in space and time in an electromagnetic wave. The oscillating electric and magnetic fields, E and B are perpendicular to each other and to the direction of propagation of the electromagnetic wave.
  • For a wave of frequency , wavelength , propagating along z-direction

Electromagnetic Waves Class 12 Notes Physics Electromagnetic Waves Class 12 Notes Physics

Electromagnetic Waves Class 12 Notes Physics  Electromagnetic Waves Class 12 Notes Physics

  • Relation between  and  : The speed c of electromagnetic wave in vacuum is related to   and  (the free space permeability and permittivity constants) as 
  • The value of c equals the speed of light obtained from optical measurements. Light is an electromagnetic wave; c is, therefore, also the speed of light. Electromagnetic waves other than light also have the same velocity c in free space.
  • Speed of Light: The speed of light, or of electromagnetic waves in a material medium is

 Where  is the permeability of the medium and  its permittivity.

  • Electromagnetic waves carry energy as they travel through space and this energy is shared equally by the electric and magnetic fields.
  • Energy Per Unit Volume: If in a region of space in which there exist electric and magnetic fields , there exists Energy Density (Energy per unit volume) associated with these fields is,
    Electromagnetic Waves Class 12 Notes Physics where we are assuming that the concerned space consists of vacuum only.
  • Electromagnetic waves transport momentum as well. When these waves strike a surface, a pressure is exerted on the surface.
  • If total energy transferred to a surface in time t is U, total momentum delivered to this surface is p = U/c.
  • Electromagnetic Spectrum: The orderly distribution of the electromagnetic waves in accordance with their wavelength or frequency into distinct groups having widely differing properties is called electromagnetic spectrum.
  • The classification has more to do with the way these waves are produced and detected.
  • Different Regions of Spectrum: Different regions are known by different names;  -rays, X-rays, ultraviolet rays, visible rays, infrared rays, microwaves and radio waves in order of increasing wavelength from or  to

(a) Radio Waves:

  •  These are produced by accelerated motion of charges in wires.
  •  These are used in radio and television communication systems.
  • These are generally in the frequency range from 500 kHz to about 1000 MHz or wavelength range 600 m to 0.1 m.

(b) Microwaves:

  • These are short wavelength radio waves with frequency range 109 Hz to 1012 Hz or wavelength range 0.3 m to 10-3 m.
  • Due to their short wavelengths, they are suitable for radar systems used in aircraft navigation.
  • Microwave ovens use them for cooking.

(c) Infrared Waves:

  • Frequency range  or wavelength range 
  • These are produced by hot bodies and molecules.
  • They lie in the low frequency or long wavelength end of the visible spectrum.

(d) Visible Light:

  • The spectrum frequency runs from about 4 x  to about 7 x  or wavelength range .
  • Our eyes are sensitive to this range of wavelengths.

(e) Ultraviolet light:

  • It covers frequency range from  or wavelengths range from .
  • The sun is an important source of UV rays.

(f) X-rays:

  • It covers frequency range from  or wavelengths range from .
  • It is used in medical diagnosis.

(g) Gamma Rays:

  • These lie in the upper frequency range Electromagnetic Waves Class 12 Notes Physics of the spectrum, and have wavelengths in the range  to .
  • It is used in manufacture of polyethylene from ethylene.

Various layers of earth’s atmosphere:
Electromagnetic Waves Class 12 Notes Physics

CBSE Class 12 Revision Notes and Key Points

Electromagnetic Waves class 12 Notes. CBSE quick revision note for class-12 Physics, Chemistry, Math’s, Biology and other subject are very helpful to revise the whole syllabus during exam days. The revision notes covers all important formulas and concepts given in the chapter. Even if you wish to have an overview of a chapter, quick revision notes are here to do if for you. These notes will certainly save your time during stressful exam days.

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