From equation (3) it can be proved that for a plane electromagnetic wave propagating along x-axis, {{\partial {E_y}} \over {\partial x}} = - {{\,\partial {B_z}} \over {\partial t}}     (4), i.e. The wavelength (λ) and the frequency (v) of electromagnetic wave is related as c = v λ = ω/ The ionosphere plays a major role in sky wave propagation. Electromagnetic waves have constant velocity in vacuum and it is nearly equal to \(3 × 10^8 m s^{-1}\) which is denoted by \(C\) = \(\frac{1}{√{μ_o ϵ_o}}\). We have considered below some of the wave propagation methods in brief. What are the directions of electric and magnetic field vectors relative to each other and relative to … Why sky wave propagation of electromagnetic waves cannot be used for TV transmission? Therefore,  {{dq} \over {dt}} = C{{dV} \over {dt}}   or   I = C{{dV} \over {dt}} Electric and magnetic fields in electromagnetic wave is of transverse nature. It has wide range with wavelength variation of 10-14 m to 6 x 102 m. Physics Important Questions Class 12 are given below. Radiant Flux Density. NCERT Solutions. At any instant, the electric and magnetic fields varying sinusoidally with x can be expressed by equation Electromagnetic Waves. Ionisation occurs due to the absorption of the ultraviolet and other high energy radiation coming from the sun, by the air molecues, The phenomenon of bending of electromagnetic waves in this layer so that they are diverted towards the earth is helpful in skywavepropogation. ( Electromagnetic Waves ) www.free-education.in is a platform where you can get pdf notes from 6th to 12th class notes, General Knowledge post, Engineering post, Career Guidelines , English Speaking Trick , How to crack interview and lots more. Jan 06, 2021 - EM Waves Properties and Propagation Class 12 Notes | EduRev is made by best teachers of Class 12. 7. Class 12th Physics – 8 Electromagnetic Waves – Notes. a magnetic field varying with time gives rise to an electric field varying in space. 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 propagation of electromagnetic waves can be shown as. The modulated signal is sent through transmitting antenna. The actual boundaries are not sharp and the distances are approximate. (a) Calculate the capacitance and the rate of change of potential difference between the plates. The whole spectrum of electromagnetic spectrum and the modern terminology used for various sections of the spectrum are shown in table. Now,   A = \pi R2 = \pi (12 x 10-2)2 = 1.44 \pi x 10-2 m2 Figure shows a capacitor made of two circular plates each of radius 12 cm and separated by 5.0 mm. 8. 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. The maximum line of sight distance (range of communication) d. Propagation of electromagnetic waves. Equation of plane progressive electromagnetic wave; E = E 0 sin ω (t – x/c) B = B 0 sin ω (t – x/c) Here, ω = 2πf. Displacement Current The current which comes into play m the region in which the electric field and the electric flux is changing with time. The average value of \vec S over a single period T is given by, S = I = {c^2}{\varepsilon _o}|{\vec E_o} \times {\vec B_o}|{1 \over T}\int\limits_0^T {{{\cos }^2}\left( {kx - \omega t} \right)} dt = {c^2}{\varepsilon _o}{E_o}\left( {{{{E_o}} \over c}} \right)\left( {{1 \over 2}} \right) = {1 \over 2}c{\varepsilon _o}E_o^2 = {1 \over {2c{\mu _o}}}E_o^2. Propagation of Electromagnetic Waves. Problem – A transmitting antenna at the top of a tower has a height of 32m and the height of the receiving antenna is 50m. Electromagnetic wave propagation does not require any material medium to travel. These waves travel through the space and reach the receiving antenna at the other end. It is given as: \(\vec{E}\times \vec{B}\). Propagation of Electromagnetic Waves. The electromagnetic waves produced: (a) will have frequency of 109 Hz. Free PDF Download of CBSE Physics Multiple Choice Questions for Class 12 with Answers Chapter 8 Electromagnetic Waves. Here {E_o} and {B_o} are the amplitudes of electric and magnetic fields along y-axis and z-axis respectively. (a)  What is the frequency in MHz and period in \mu s in vacuum? Displacement current is that which results due to the displacement of electrons. 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, \vec E = {\vec E_o}\cos \left( {kx - \omega t} \right)      and     \vec B = {\vec B_o}\cos \left( {kx - \omega t} \right), Then radiant flux density \vec S is given by, \vec S = {c^2}{\varepsilon _o}\left( {\vec E \times \vec B} \right) = {c^2}{\varepsilon _o}{\vec E_o} \times {\vec B_o}{\cos ^2}\left( {kx - \omega t} \right), Hence |\vec S| = {c^2}{\varepsilon _o}|{\vec E_o} \times {\vec B_o}|{\cos ^2}\left( {kx - \omega t} \right). Given c = 3 x 108 m/s. At any instant, the electric and magnetic fields varying sinusoidally with x can be expressed by equation, Faraday's law of electromagnetic induction states that. An accelerated charge acts as the source of electromagnetic waves. Various regions do not have sharply defined boundaries. Class-12CBSE Board - Propagation of electromagnetic waves - LearnNext offers animated video lessons with neatly explained examples, Study Material, FREE NCERT Solutions, Exercises and Tests. from y-rays to radio waves. An accelerated charge acts as the source of electromagnetic waves. The magnetic field is perpendicular to the direction of propagation as well as to the electric field E. It is given by, Maxwell discovered the concept of displacement current. 1. Electromagnetic waves are transverse in nature. Electromagnetic waves- features Waves generally require a material medium for their propagation. The magnetic field is perpendicular to the direction of propagation as well as to the electric field E. It is given by, B = {B_o}\sin \omega \left( {t - x/c} \right). Dronstudy provides free comprehensive chapterwise class 12 physics notes with proper images & diagram. Students can solve NCERT Class 12 Physics Electromagnetic Waves MCQs Pdf with Answers to know their preparation level. These waves travel through the space and reach the receiving antenna at the other end. Therefore, velocity of light in glass \nu = {c \over \mu } = {{3 \times {{10}^8}} \over {1.5}} = 2 \times {10^8}m/s Download NCERT Books, Video Lectures ASK DOUBTS Start Discusssion Free JEE Test Series, Get the most advanced study material and top your exams. (d) Total average energy density, {u_E} + {u_B} = 2{u_E} = 2{u_B} = {1 \over 2}{\varepsilon _o}E_o^2 = {1 \over 2}{{B_o^2} \over {{\mu _o}}}, 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 charging current is constant and is equal to 0.15 A. Electromagnetic Waves. var m = now.getMinutes(); The total radiant flux emitted at any instant is given by, When an electromagnetic wave advances, the electromagnetic energy flows in the direction of, 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. Such a combination of mutually perpendicular electric and magnetic fields is referred to as an electromagnetic wave in vacuum. Electromagnetic waves with a wavelength of the order of a few meters were first produced and detected in the laboratory by Hertz in 1887. Class 12 Physics Electromagnetic Waves: Nature of EM waves: Nature of EM waves. Class 10 Class 12. Class 10 Class 12. Given that {\varepsilon _0} = 8.85 \times {10^{ - 12}}{C^2}{N^{ - 1}}{m^{ - 2}}. Electric field is varying with time, and it will give rise to magnetic field, this magnetic field is varying with time and it gives rise to electric field and the process continues so on. This phenomenon of loss of power of the ground wave is called attenuation, The attenuation of ground waves increases very rapidly with the increase in its frequency, Thus, ground wave communication is not suited for high frequency signal wave and for very long range communication, To radiate signals with high efficiency, the antennas should have a size comparable to the wavelength of the signal. While communication using radio waves, the transmitter antenna radiates electromagnetic waves. It is an electromagnetic wave, therefore the correct choice is (a). Electromagnetic waves are coupled time varying electric and magnetic fields that propagate in space. It also bends around the corner of the objects on the earth, Due to this, the energy of the ground wave is gradually absorbed by the earth and the power of the ground wave decreases, The power of the ground wave decreases with the increase in the distance from the transmitting station. Various layers in which the atmosphere has been divided are shown in figure. There is also a sinusoidally varying magnetic field associated with electric field when light propagates. 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. (iv) EM waves are produced by accelerating charged particle. Physics Electromagnetic Waves part 1 (Introduction) CBSE class 12. The line of sight distance is the distance between transmitting antenna and receiving antenna at which they can see each other. From equation (1), we have, {{\partial {E_y}} \over {\partial x}} = {E_o}\cos \left( {x - ct} \right), {{\partial {B_y}} \over {\partial t}} = - c{B_o}\cos \left( {x - ct} \right), Substituting for {{\partial {E_y}} \over {\partial x}}  and {{\partial {B_z}} \over {\partial t}}  in equation (1), {E_o} = c{B_o}     or     c = {{{E_o}} \over {{B_o}}}, It shows that the velocity of electromagnetic waves is equal to the ratio of amplitudes of electric and magnetic fields. Physics Class 12 Important Questions are very helpful to score high marks in board exams. document.write(''); Free PDF Download of CBSE Physics Multiple Choice Questions for Class 12 with Answers Chapter 8 Electromagnetic Waves. Physics MCQs for Class 12 Chapter Wise with Answers PDF Download was Prepared Based on Latest Exam Pattern. (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. Electromagnetic Waves. Class 9 - Science+Maths Video Paper Solutions, Class 10 - Science+Maths Video Paper Solutions, 11+12 - Physics + Chemistry + Mathematics, 11+12 - Physics + Chemistry + Mathematics (IIT), 11+12 - Physics + Chemistry + Biology (NEET), Class 9th and 10th : Foundation for IIT Physics, Class 9th and 10th : Foundation for IIT Chemistry, How to make the best choice: Science vs Commerce vs Arts, How to Study Effectively- 9 Secrets No One Tells, How to prepare for IIT-JEE this summer - Top 7 proven ways. (c)  Is Kirchhoff's first rule valid at each plate of the capacitor? Velocity of light, c = 3 x 108 m/s Answer . (a) The capacitance of parallel plate capacitor is given by, C = {{{\varepsilon _o}A} \over d} = {{8.85 \times {{10}^{ - 12}} \times 1.44\pi \times {{10}^{ - 2}}} \over {5 \times {{10}^{ - 3}}}} = 80.1 \times {10^{ - 12}}V, Now, q = CV (b) Displacement current is equal to conduction current i.e. document.write(''); The constant c is the speed of light in vacuum. The S. I. unit of S is watt/(metre)2. Need for Displacement Current Ampere’s circuital law for conduction current during charging of a capacitor was found inconsistent. document.write(''); Here,   d = 5.0 mm = 5.0 x 10-3 m; R = 12 cm = 12 x 10-2 m, I = 0.15 A. \oint {\vec E.d\vec s} = q/{\varepsilon _o}, 3. Faraday's Law of Electromagnetic Induction, \varepsilon = - {{d{\Phi _B}} \over {dt}}  or  \oint {\vec E.d\vec l = - {{d{\Phi _B}} \over {dt}}}, \oint {\vec B.d\vec l} = {\mu _o}\left( {{I_C} + {\varepsilon _o}{{d{\Phi _E}} \over {dt}}} \right). Class ---Class 6Class 7Class 8Class 9Class 10Class 11Class 12IIT-JEEAIPMT/NEET They do not require any material medium for their propagation. The actual boundaries are not sharp and the distances are approximate. (iii) The electric and magnetic field variation are in phase. 673 Views. The linear momentum carried by the portion of wave having energy U is given by. Chapter 8 Electromagnetic Waves Class 12 th Physics deals with various types of radiations sustaining in the environment. The generalized form of Ampere's law \oint {B.dl} = {\mu _o}I, which includes both conduction current {I_C} (current flowing through the conducting wire) and displacement current {I_C} as given by Maxwell i.e. and {I_D} = {\varepsilon _o}{{d{\Phi _E}} \over {dt}} Various layers in which the atmosphere has been divided are shown in figure. (b)  Obtain the displacement current across the plates. This video will make you understand about the Electromagnetic Waves basic concept. Electromagnetic Spectrum is the orderly distribution of electromagnetic radiations according to their wavelength or frequency. Therefore modified Ampere's law may be expressed as, \int {\vec B.d\vec l} = {\mu _o}\left( {{I_C} + {\varepsilon _o}{{d{\Phi _E}} \over {dt}}} \right). In this way, electric and magnetic fields of the wave sustain each other. 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