(c)  Is Kirchhoff's first rule valid at each plate of the capacitor? The wave equation for light propagating in x-direction in vacuum may be written as, E = {E_o}\sin \omega \left( {t - x/c} \right), where E is the sinusoidally varying electric field at position x at time t. The constant c is the speed of light in vacuum. Free PDF Download of CBSE Physics Multiple Choice Questions for Class 12 with Answers Chapter 8 Electromagnetic Waves. He thus verified a basic prediction of Maxwell’s equations. 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. 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. According to Maxwell, the electromagnetic waves are those waves in which there is a sinusoidal variation of electric and magnetic field vectors are at right angles to each other, and the direction of wave propagation. Class 12th Physics – 8 Electromagnetic Waves – Notes. Physics Important Questions Class 12 are given below. Balbharati Solutions (Maharashtra) ... CBSE Previous Year Question Paper With Solution for Class 12 Arts; Free PDF Download of CBSE Physics Multiple Choice Questions for Class 12 with Answers Chapter 8 Electromagnetic Waves. The wavelength(λ) and frequency (v) of the EM waves can be related as: c= v.λ. Given c = 3 x 108 m/s. The generalized form of Ampere's law, Therefore modified Ampere's law may be expressed as, (a) The capacitance of parallel plate capacitor is given by. Displacement current is that which results due to the displacement of electrons. Displacement Current The current which comes into play m the region in which the electric field and the electric flux is changing with time. Physics Electromagnetic Waves part 1 (Introduction) CBSE class 12. from y-rays to radio waves. The intensity of electromagnetic wave is, I = {{{P_{av}}} \over {4\pi {r^2}}} = {u_{av}} \times c = {1 \over 2}{\varepsilon _o}E_o^2c = {1 \over {2{\mu _o}}}B_o^2c = {1 \over {2{\mu _o}}}. While communication using radio waves, the transmitter antenna radiates electromagnetic waves. Download NCERT Books, Video Lectures ASK DOUBTS Start Discusssion Free JEE Test Series, Get the most advanced study material and top your exams. 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. document.write(''); The constant c is the speed of light in vacuum. function checkTime(i) { (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. Velocity of electromagnetic waves is also given by, c = {1 \over {\sqrt {{\mu _o}{\varepsilon _o}} }}. Why sky wave propagation of electromagnetic waves cannot be used for TV transmission? An accelerated charge acts as the source of electromagnetic waves. Why sky wave propagation of electromagnetic waves cannot be used for TV transmission? Ozon layer: The upper region of stratosphere is rich in ozone and is called ozone layer. These waves travel through the space and reach the receiving antenna at the other end. This document is highly rated by Class 12 students and has been viewed 1521 times. The S. I. unit of S is watt/(metre)2. 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. What is the maximum distance between them for satisfactory communication in LOS mode? (x) Intensity of electromagnetic wave is defined as energy crossing per unit area per unit time perpendicular to the directions of propagation of electromagnetic wave. Therefore,  {{dq} \over {dt}} = C{{dV} \over {dt}}   or   I = C{{dV} \over {dt}} s = checkTime(s); It helps us to categorize various waves based on their frequency, wavelength, uses, and origin. Propagation of Electromagnetic Waves. (xii) The existence of electromagnetic waves was confirmed by Hertz experimentally in 1888. Electromagnetic Waves. MCQs. Electromagnetic waves with a wavelength of the order of a few meters were first produced and detected in the laboratory by Hertz in 1887. It is given as: \(\vec{E}\times \vec{B}\). Electromagnetic Waves Class 12 Notes Chapter 8. An oscillating charge in an LC circuit also produces EM waves. Electromagnetic Spectrum is the orderly distribution of electromagnetic radiations according to their wavelength or frequency. We know Physics is tough subject within the consortium of science subjects physics is an important subject.But if you want to make career in these fields like IT Consultant, Lab Technician, Laser Engineer, Optical Engineer etc. CBSE Class 12 Physics Electromagnetic Waves Important Questions. The average value of pointing vector (\vec S) over a convenient time interval in the propagation of electromagnetic wave is known as radiant flux density. Velocity of light, c = 3 x 108 m/s 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. Zigya App. Electromagnetic Waves – Notes. Therefore, Maxwell modified Ampere’s circuital law. It is also called range of communication d. The range of space wave communication can be increased by increasing the heights of the transmitting antenna and receiving antenna. and {I_D} = {\varepsilon _o}{{d{\Phi _E}} \over {dt}} Physics MCQs for Class 12 Chapter Wise with Answers PDF Download was Prepared Based on Latest Exam Pattern. the electromagnetic waves are radiated out by the transmitter antenna at one place which travel through the space and reach the receiving antenna at the other place. (a)  If \nu is the frequency, then, \nu = {c \over \lambda } = {{3 \times {{10}^8}} \over {5.5 \times {{10}^{ - 7}}}} Hz = {{3 \times {{10}^8}} \over {5.5 \times {{10}^{ - 7}} \times {{10}^6}}} = 5.45 \times {10^8} MHz, T = {1 \over \mu } = {\lambda \over c} = {{5.5 \times {{10}^{ - 7}}} \over {3 \times {{10}^8}}} = 1.8 \times {10^{ - 15}} \times {10^6} = 1.8 \times {10^{ - 19}}\mu s, (b) Now, refractive index \mu = {{{\rm{veloicty of light in vacuum}}} \over {{\rm{velocity}}{\mkern 1mu} {\mkern 1mu} {\rm{of light in glass}}}} = {c \over \nu } The four basic laws of electricity and magnetism i.e. The process by which an audio signal is superimposed over the carrier waves is known as modulation. Electromagnetic wave equation describes the propagation of electromagnetic waves in a vacuum or through a medium. (b) Displacement current is equal to conduction current i.e. Suggest two methods by which range of TV transmission can be increased. 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. When energy of electromagnetic wave is incident on a surface, the flux density is called intensity of wave (denoted by I). (b) Displacement current is equal to conduction current i.e. 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). Light may be described as a wave. var h = now.getHours(); Electromagnetic Waves. Electromagnetic wave propagation does not require any material medium to travel. The range varies from 10 -12 m, to 10 4 m, i.e. These waves required no medium for its propagation. document.write(''); Propagation of Electromagnetic Waves. Class-12CBSE Board - Propagation of electromagnetic waves - LearnNext offers animated video lessons with neatly explained examples, Study Material, FREE NCERT Solutions, Exercises and Tests. (c) at rest. Electromagnetic Waves Class 12 Notes Chapter 8. Need for Displacement Current Ampere’s circuital law for conduction current during charging of a capacitor was found inconsistent. Propagation of Electromagnetic Waves. Electromagnetic waves are transverse in nature. At some point by the curvature of the earth, the line of sight propagation gets blocked. and   {B_Z} = {B_o}\sin \left( {x - ct} \right)     (2) 1. These waves required no medium for its propagation. … It shows that the velocity of electromagnetic waves is equal to the ratio of amplitudes of electric and magnetic fields. Answer . Question 1. Electromagnetic Wave Equation. We know that the earth’s atmosphere is divided into various regions like – Troposphere, Stratosphere, Mesosphere and Ionosphere. 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. The direction of propagation of the electromagnetic wave is given by vector cross product of the electric field and magnetic field. (b) will have frequency of 2 × 109 Hz. Textbook Solutions. It helps us to categorize various waves based on their frequency, wavelength, uses, and origin. Concept: ... Electromagnetic Waves video tutorial 01:01:41; Advertisement Remove all ads. a magnetic field varying with time gives rise to an electric field varying in space. 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. Problem – A transmitting antenna at the top of a tower has a height of 32m and the height of the receiving antenna is 50m. The signal wave glides over the surface of the earth, While propagating on the surface of the earth, the ground wave induces current in the ground. These waves travel through the space and reach the receiving antenna at the other end. The charging current is constant and is equal to 0.15 A. Answer . Radiant Flux Density. (c) will have a wavelength of 0.3 m. (d) fall in the region of radiowaves. The transverse waves are those in which direction of disturbance or displacement in the medium is perpendicular to that of the propagation of wave. It is an electromagnetic wave, therefore the correct choice is (a). The average value of pointing vector () over a convenient time interval in the … The wavelength (λ) and the frequency (v) of electromagnetic wave is related as c = v λ = ω/ Class 12 Physics Communication Systems. 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). var s = now.getSeconds(); Hence, space waves are used for line of sight communication such as television broadcast, microwave link and satellite communication, The line of sight communication is limited by (a) the line of sight distance (b) the curvature of the earth. The ionosphere is also called as thermosphere as temperature increases rapidly here and it is the outermost part of the earth’s atmosphere, Above troposphere, we have various layers like D (part of stratosphere), E (part of stratosphere), F, The ionosphere is called so because of the presence of large number of ions or charged particles. Class 12 Physics Electromagnetic Waves: Nature of EM waves: Nature of EM waves. While communication using radio waves, the transmitter antenna radiates 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. m = checkTime(m); P = {q^2}{a^2}/(6\pi {\varepsilon _0}{c^3}), where q is the charge on the particle and a is its instantaneous acceleration. Given that {\varepsilon _0} = 8.85 \times {10^{ - 12}}{C^2}{N^{ - 1}}{m^{ - 2}}. It is an electromagnetic wave, therefore the correct choice is (a). } 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. Example 1 It has wide range with wavelength variation of 10-14 m to 6 x 102 m. Due to which the electromagnetic waves incident on a surface exert a force on the surface. Electromagnetic Waves. The capacitor is being charged by an external source (not shown in the figure). Displacement Current The current which comes into play m the region in which the electric field and the electric flux is changing with time. Each electromagnetic wave has its characteristic properties and features. If distributive inference occurs at the receiving end. = {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. = {c^2}{\varepsilon _o}{E_o}{B_o}\sin {90^o}\left[ {{1 \over 2}} \right]                     [since {1 \over T}\int\limits_0^T {{{\cos }^2}\left( {kx - \omega t} \right)} dt = {1 \over 2} ] a magnetic field varying with time gives rise to an electric field varying in space. 1. Figure shows a capacitor made of two circular plates each of radius 12 cm and separated by 5.0 cm. The actual boundaries are not sharp and the distances are approximate. Electromagnetic Waves. 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. CBSE Notes of Class 12 Physics Electromagnetic Waves Introduction. or   {{dV} \over {dt}} = {1 \over C} = {{0.15} \over {80.1 \times {{10}^{ - 12}}}} = 1.873 \times {10^9}V{s^{ - 1}}. The maximum line of sight distance (range of communication) d. Electromagnetic Spectrum The systematic sequential distribution of electromagnetic waves in ascending or descending order of frequency or wavelength is known as electromagnetic spectrum. Example 2 var month = ("0" + (now.getMonth() + 1)).slice(-2); Various layers in which the atmosphere has been divided are shown in figure. Various layers in which the atmosphere has been divided are shown in figure. Concept: ... Electromagnetic Waves video tutorial 01:01:41; Advertisement Remove all ads. (x) Intensity of electromagnetic wave is defined as energy crossing per unit area per unit time perpendicular to the directions of propagation of electromagnetic wave. Notes for Electromagnetic Waves chapter of class 12 physics.