What is Em waves: Definition and 226 Discussions

In physics, electromagnetic radiation (EM radiation or EMR) refers to the waves (or their quanta, photons) of the electromagnetic field, propagating through space, carrying electromagnetic radiant energy. It includes radio waves, microwaves, infrared, (visible) light, ultraviolet, X-rays, and gamma rays. All of these waves form part of the electromagnetic spectrum.Classically, electromagnetic radiation consists of electromagnetic waves, which are synchronized oscillations of electric and magnetic fields. Electromagnetic radiation or electromagnetic waves are created due to periodic change of electric or magnetic field. Depending on how this periodic change occurs and the power generated, different wavelengths of electromagnetic spectrum are produced. In a vacuum, electromagnetic waves travel at the speed of light, commonly denoted c. In homogeneous, isotropic media, the oscillations of the two fields are perpendicular to each other and perpendicular to the direction of energy and wave propagation, forming a transverse wave. The wavefront of electromagnetic waves emitted from a point source (such as a light bulb) is a sphere. The position of an electromagnetic wave within the electromagnetic spectrum can be characterized by either its frequency of oscillation or its wavelength. Electromagnetic waves of different frequency are called by different names since they have different sources and effects on matter. In order of increasing frequency and decreasing wavelength these are: radio waves, microwaves, infrared radiation, visible light, ultraviolet radiation, X-rays and gamma rays.Electromagnetic waves are emitted by electrically charged particles undergoing acceleration, and these waves can subsequently interact with other charged particles, exerting force on them. EM waves carry energy, momentum and angular momentum away from their source particle and can impart those quantities to matter with which they interact. Electromagnetic radiation is associated with those EM waves that are free to propagate themselves ("radiate") without the continuing influence of the moving charges that produced them, because they have achieved sufficient distance from those charges. Thus, EMR is sometimes referred to as the far field. In this language, the near field refers to EM fields near the charges and current that directly produced them, specifically electromagnetic induction and electrostatic induction phenomena.
In quantum mechanics, an alternate way of viewing EMR is that it consists of photons, uncharged elementary particles with zero rest mass which are the quanta of the electromagnetic field, responsible for all electromagnetic interactions. Quantum electrodynamics is the theory of how EMR interacts with matter on an atomic level. Quantum effects provide additional sources of EMR, such as the transition of electrons to lower energy levels in an atom and black-body radiation. The energy of an individual photon is quantized and is greater for photons of higher frequency. This relationship is given by Planck's equation E = hf, where E is the energy per photon, f is the frequency of the photon, and h is Planck's constant. A single gamma ray photon, for example, might carry ~100,000 times the energy of a single photon of visible light.
The effects of EMR upon chemical compounds and biological organisms depend both upon the radiation's power and its frequency. EMR of visible or lower frequencies (i.e., visible light, infrared, microwaves, and radio waves) is called non-ionizing radiation, because its photons do not individually have enough energy to ionize atoms or molecules or break chemical bonds. The effects of these radiations on chemical systems and living tissue are caused primarily by heating effects from the combined energy transfer of many photons. In contrast, high frequency ultraviolet, X-rays and gamma rays are called ionizing radiation, since individual photons of such high frequency have enough energy to ionize molecules or break chemical bonds. These radiations have the ability to cause chemical reactions and damage living cells beyond that resulting from simple heating, and can be a health hazard.

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  1. R

    Can a sinusoidal EM wave exist in nature?

    I saw an example of a hypothetical EM wave that had constant E and B fields. Is that possible? How would it be produced? And wouldn't such a wave have an infinite wavelength?
  2. S

    Explaining Electric and Magnetic Fields in EM Waves

    Hi, I've read that the speed of em waves in the vacuum is the electric field component frac the magnetic field component, why and how can this be explained more easily ? Thanks
  3. F

    How Fast Do EM Waves Travel in Ferromagnetic Materials?

    Homework Statement An EM wave with frequency 87Mhz travels in an insulating ferromagnetic material with \mu_0 \mu_r = 1000 and \epsilon_0 \epsilon_r = 10 - What is the speed of the EM wave in the material. Homework Equations v=(\sqrt{\mu_0 \mu_r \epsilon_0 \epsilon_r})^{-1} The Attempt at a...
  4. F

    Does non-sinusoidal electric/magnetic fields generate EM waves

    why all EM waves are sinusoidal ? or this is not true at all, i.e., EM waves of other waveforms do exist ? the above 2 questions are among the most vague in classical EM theory, of which i studied many topics in collage as an electrical engineering student, and i liked the subject so i kept...
  5. F

    Does the Drude model predict the emission of em waves?

    The Drude model of electrical conduction has the charge carriers being accelerated by an electric field and then interacting with the lattice ions. The cycle is then repeated. An unbound charged particle if accelerated emits electromagnetic waves. Does that mean that a prediction of the Drude...
  6. V

    EM Waves & Forces: Does a Particle Feel Force?

    Would a particle kept in the path of an electromagnetic wave experience a force? Both magnetic and electric field are present, so the equation of motion may be complex, but i have never seen my textbook refer to the the possibility of an em wave causing a charged particle to move.
  7. L

    Can High Frequency Signals Flow Without a Medium?

    EM waves do not need a medium for propagation. But isn't high frequency signal (like USB) flowing in a wire also electromagnetic. How come it needs copper as a medium.
  8. Crazymechanic

    Can EM Waves Levitate Objects in a Transparent Plasma?

    Hi, recently I saw a great video about some scientists levitating small objects in mid air by trapping them in overlapping 180 degrees out of phase sine waveforms. It is easy to see that air is the medium through which sound can travel and sounditself being the vibration of air traps these...
  9. U

    Solve EM Wave Vacuum Homework: Prove Relation, Find B, Reflect Wave Form

    Homework Statement EM Waves propagating through vacuum towards the x-direction approaches a conducting surface at x = 0. Part (a): Prove the following relations. Find the boundary conditions for E and B if charge density σ and current density s exists on the surface. Part (b): Find B in...
  10. U

    EM Waves in Transmission lines

    Homework Statement (a) Find the capacitance per unit length and find the inductance per unit length of a transmission wire above a infinite conducting plane. I used the image method (b) Show that EM waves can propagate, and find their speed and the characteristic impedance of the line...
  11. N

    Moire pattern and interference of plane EM waves

    Homework Statement Look at the Moire pattern in "Oppgave 5" (assignment 5) in the attached pdf file. The Moire pattern you see is supposed to represent the interference between two plane EM waves whose directional ##\vec{k}## vectors form an angle ##\theta## with each other. Anyway, the main...
  12. C

    Dispersion Relation for EM Waves: Skin Depths in Good and Poor Conductors

    Homework Statement The following dispersion relation is obtained by substituting a plane wave solution for ##\mathbf{B}## into $$\nabla^2 \mathbf{B} = \mu \epsilon \frac{\partial^2 \mathbf{B}}{\partial^2 t} + \mu \sigma \frac{\partial \mathbf{B}}{\partial t}:$$ $$\hat{k} = (\mu \epsilon w^2 +...
  13. K

    EM waves- self propagating in a vacuum?

    First of all, I understand that an EM wave is created by a charged particle that is moving. What I don't understand is how it propagates itself when traveling through a vacuum as there is no medium for it to interact with. Can this be explained by anything other than photon theory? I really...
  14. K

    Do Quarks Create EM Waves? Exploring the Connection

    Do quarks cause EM waves?
  15. S

    EM waves: energy and power related to frequency

    Hello, I was reading articles about EMR and health and I realized I never got how "output power" is related to frequency. Let's talk about energy, the rule is: the higher the frequency (shorter wavelength) the higher is the energy transported by the wave. Now power, power is the energy...
  16. D

    Reason behind speed of em waves being constant

    Do we have any understanding as to why em waves have same speed in all inertial frames?
  17. N

    Power of EM Wave Absorbed by Circular Disk of Radius 2m

    Homework Statement A plane polarized electromagnetic wave propagates with Erms = 30 V/m. What is the power transmitted to a circular disk of radius r = 2m, if all of the light is absorbed by the disk and S is perpendicular to the disk? Homework Equations There is a passage that goes...
  18. C

    Help with EM waves travelling through a plasma

    I've been given a practice question for an exam and I can't quite get it started. The question is: Intelligent beings on a distant planet try and communicate with Earth by sending powerful radio waves swept in frequency from 10 to 50MHz per minute. The linearly polarized emissions must pass...
  19. mesa

    EM Waves, how are they created?

    A moving charge creates a Bf so is an EM wave created (for example) by an electron oscillating in a conductor producing a changing Bf which then induces an Ef with both perpendicular to the direction of propagation? If so I am presuming the point where the Bf crosses the axis represents the...
  20. Y

    What happens to EM waves outside the universe?

    If the universe is expanding at less than the speed of light, what happens to EM radiation that is emitted from stars at the edge of the universe?
  21. cryora

    EM waves and the direction of E-fields & B-Fields

    What I'm wondering is whether or not the E-fields and B-fields making up an EM wave always point outwards. Would it be possible to have an EM wave where either the E-fields or B-fields, or both, point inwards towards the path of propagation? The only diagrams I see in books and the internet...
  22. H

    Cherenkov radiation Why the EM waves are constructive

    I was reading an article about Cherenkov radiation in wikipedia. If the electron moves slower than light the EM waves in the medium are destructive and if they travel faster than light waves are constructive .Why so?When the electron travels faster than light the radiations cannot interfere...
  23. R

    Attenuation of em waves- unknown relationship help.

    Sorry if this is in the wrong place. Was not sure what it is categorised as. I have come across the following:e^{-\frac{\omega}{c} nkz}, referring to attenuation of a wave. It was found here...
  24. V

    Couple of Questions Regarding EM Waves

    I'm a little unsure of my own answers to these questions. Hopefully I'll clear up my misconceptions. 1. If I measure the E-field and B-field at a point in space where there is an EM wave, would I be able to determine the direction it propagates from? My Ans: I don't think so, since when...
  25. E

    Interaction of EM waves with matter

    The interaction of light with matter, or EM waves in general, falls into 3 categories: transparent where they pass through, opaque where they are scattered, and shiny where they are reflected. What on the quantum mechanical level about the atoms electrons determines those properties? I think the...
  26. A

    Conceptual difficulties with the generation and description of EM waves

    Hello all, I had a question about Electromagnetic waves. Although it isn’t homework (just to settle something in my own mind) I thought this would be the best place to put it. Perhaps it would be best if I could explain a situation I could understand and then hopefully someone could bridge...
  27. B

    EM waves: multiple planar interfaces (PEC-backed lossy dielectric)

    Homework Statement Our prof has told us we can get help from wherever/whoever we want as long as it isn't classmates. This is a take-home test. The relevant question: You have a three-layer dielectric. | Layer 1 | Layer 2 | Layer 3 | Layers 1 and 3 are semi-infinite. Layer 1 is air (εr =...
  28. M

    Is Computing Using Electromagnetic Waves Possible?

    Hi all, I was just wondering if there has been research into computing using electromagnetic waves. It seems to me like a sealed off box with internal EM pluses could be used to mould waveforms through interference, which would act as logic gates to provide useful computational results. Would...
  29. A

    EM waves and blackbody radiation question

    Homework Statement A rectangular metal plate measures 0.20 m long and 0.3 m wide. The plate is heated to a temperature of 1,433 K by passing a current through it. Assuming that it behaves like a blackbody, how much power does the plate radiate under these conditions? Homework Equations...
  30. R

    Complex Representation of Moving EM Waves

    Homework Statement Moving in negative x-axis: E1 = E sin(wt + kx) Moving in right axis: E2 = Esin(wt-kx-θ) moving to right write complex representation The Attempt at a Solution E1= E Im(exp[i*(wt+kx)]) E2= E Im(exp[i*(wt-kx-θ)]) are these correct or do I have to take into...
  31. D

    How Do You Solve EM Wave Transmission Through Multiple Media?

    Hi there, I'm stuck with this problem, I've already worked out some algebra but I can't seem to get what I am asked, when trying to solve the equations I simply can't get the answer, so I was hoping you could help me. Here we go Homework Statement Calculate the transmission coefficient T...
  32. J

    How are soundwaves sent via em waves?

    When the mic hears the noise, it creates an alternating current electrical signal right? So how does that translate to em waves? Is it just that a higher frequency radio wave length would resemble a higher pitch? If so, is it impossible to hear the pitch "produced" by, say, visible light?
  33. J

    If EM waves travel forever, why do things get dimmer as they get further away?

    Other than nearby light pollution. Or is that the only reason?
  34. A

    EM Wave Creation and Physical Characteristics

    My book seems to not go into a lot of details as to how EM-waves are created. More or less they just state that they are created by accelerated charges. I guess that somehow makes sense since an accelerated charge is clearly altering the electric field everywhere in space and that is as far as I...
  35. S

    Is speed of em waves directly proportional to magntiude of wavelength

    I read that speed is directly proportional to wavelength in a medium. so does it mean that gamma is the slowest in air compared to the rest of the waves?
  36. A

    Exploring the Feasibility of Using EM Waves for Long-Distance Heating of Metals

    Is it possible (and practical) to use electromagnetic waves to heat copper (or other metals such as iron, steel or an aluminium alloy) over long distances (such as 1km)?
  37. T

    What happens when two EM waves collide on matter?

    I was wondering, if two EM waves of the same freq could add via superposition ON THE SAME ELECTRON or atom (at the same time) to become ionizing? For argument's sake say if each wave was just below UV I remember E = hf, which would indicate no, I don't see how the energy would not add...
  38. P

    Accelerating charged particles emit EM waves?

    I know that if you have alternating current in a wire, it will produce electromagnetic waves since the electric and magnetic field change direction continuously as the wave propagates, and that the wave direction, orientation of the E component, and orientation of the B component will all be...
  39. M

    Speed of EM waves in a baseball park setting

    Homework Statement You and a friend are sitting in the outfield bleachers of a baseball park 140m from homeplate. The temperature is 20*C. YOur friend is listening to radio comentary with headphones while watching. There is a microphone located 17m from home plate to pick up the sound as the...
  40. S

    Does Hubble's Expansion voilate conservation of energy by redshifting EM waves?

    I am assuming the answer to my question is no, but what am I missing? My reasoning is very basic: E=hf, therefore as the universe expands the wavelength of all the far traveling radiation is increased and due to constant velocity c their frequency must decrease which translates into them losing...
  41. M

    Exploring the Medium of EM Waves: Dark Matter?

    So, I have been doing a lot of reading. I have an 8 year old girl that has renewed my interest in physics, chemistry, biology, etc. I find it interesting that we say that Electromagnetic Waves travel through a vacum. We know that mechanical waves like those propagated in liquids and gas...
  42. B

    What is the formula for calculating average power of electromagnetic waves?

    Homework Statement Homework Equations Savg = Em * Bm / (2*μ0 * c) The Attempt at a Solution I solved for S avg without calculating inside the cos, but I got it right. The z and t is given, but is there the reason why you don't solve inside the cos, or is it the bug? it's...
  43. S

    What Determines the Polarization of EM Waves?

    Hi I don't understand the polarization of EM waves. I have same questions about that. 1-) As you know, EM wave is consist of both electric and magnetic field/wave. And there is 90 degree between them. Is that possible to separate these two fields or waves? I mean is that rule: If there is...
  44. jaketodd

    Materials that radio frequency EM waves can penetrate

    Can radio waves penetrate steel? What about titanium? Maybe a characterization of what they can't penetrate would be more informative? ...Or a way to figure out what materials they can penetrate. Thanks, Jake
  45. C

    EM Waves in Conductors: Why Does B Field Lag E Field?

    When an EM wave goes in a conductor it says that the B field component lags the E field component, What causes this? I looked in Griffiths and I couldn't find the answer. Does it have something to do with the fact that when the EM wave enters the conductor it is moving the free electrons in the...
  46. S

    Why do electromagnetic waves oscillate?

    Hi everyone, I have a specific question regarding the nature of electromagnetic waves. I understand he basics of EM waves (frequency, amplitude, wavelength, etc.) and that 'it' is a pair of oscillating fields; one electric and one magnetic, perpendicular to the direction of travel. What I...
  47. H

    Exploring the Mysteries of EM Waves in Space

    Hi, I am not a student of physics, asking the question as it came to mind as I read certain articles: 1. When EM Waves is emitted by a source say star it spreads in vacuum. How does the waves Stretch? What fills in the gaps as the sphere of spread grows? If light emission is continuous...
  48. ElijahRockers

    Visualizing EM Waves: Learn Basics in 9 Days

    Perhaps this is going in the wrong forum, but the Math and Science Learning Materials forum would not let me create a new topic. I am not necessarily worrying about a specific question; in fact I am able to use the equations and formulas relevant to electromagnetic waves in my physics course...
  49. X

    EM waves, Light, radio and all that.

    I find EM waves very intriguing. But i get more confused and new questions pop up in my head every time i read something about it. I have a few basic questions. 1. Wavelength: As wavelength is distance between two peaks, how can we measure this distance in cm, meter etc. as physically there...
  50. F

    EM waves and conducting surfaces

    Firstly, I'm a bit confused about EM wave propagation. Take the picture you see everywhere illustrating the perpendicularity of E and B in a traveling EM wave (like this http://web.onetel.net.uk/~gdsexyboy/em_wave.jpg) -- does that actually illustrate the magnitudes of E and B at a particular...
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