What is Em radiation: Definition and 89 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. Vectronix

    B Electromagnetic radiation interacting with a magnetic field

    Why isn't EM radiation attracted/repelled by a magnetic field?
  2. J

    I Interaction of EM radiation with Glass

    Hi, I wanted some clarification on the mechanism for how EM radiation interacts with standard glass, namely IR, visible and high energy (UV and X-ray). Looking online most sources seem to say the band gap is around 10eV. Since visible light is about 1-3eV visible light will be transmitted. IR...
  3. V

    B Why does charge oscillate in an electric dipole antenna?

    Picture: Energy source => LR Oscillator => Transformer => Transmission line => Electric dipole antenna => traveling wave Why would the charge even oscillate in the antenna as opposed to building up in the antenna? The transmission line + antenna is not a closed circuit right?
  4. J

    B EM Radiation Amplitude: Is Peak Related to Intensity?

    Electromagnetic radiation is propagating sinusoidal electric and magnetic fields. Are the peak amplitudes of these fields in any way related to the radiation's other parameters, e.g. its instensity?
  5. N

    B EM radiation creation within stars

    Having had a look at the following video of the dipole antenna and the creation of EM radiation, which I completely understand, I had a look at the link http://hyperphysics.phy-astr.gsu.edu/hbase/Astro/procyc.html#c1 and the hydrogen fusion process within a star. Looking at the process how do...
  6. T

    In what class does one typically learn that atoms emit EM radiation?

    I took Inorganic Chemistry I and Physics in high school. I took Inorganic Chemistry I and about half of Inorganic Chemistry II (dropped out mid-semster of Inorganic Chemistry II) in college. My Physics class in high school was just regular physics, not AP Physics, so I have never taken a...
  7. H

    Exploring the Conditions for EM Radiation: Free Electrons vs Bound Electrons

    Suppose there are two free electrons. Their mutual repulsion causes each to accelerate. Is there EM radiation? Suppose those electrons are loosely bound to a nucleus, as in a metal. Is there EM radiation?
  8. A

    EM radiation temperature vs particle temperature

    I just realized I'm having a problem in understanding this. So let's take an example the CMB is around 160 Ghz and the blackbody temperature within this frequency range is 2.7K which is rather cold as it is close to absolute zero. Then let's take another example, Iter plasma will achieve about...
  9. bhobba

    Exploring the Evidence for Visible Light as EM Radiation

    Hi All In discussing another issue it occurred to me the only experiential evidence I know that normal visible light is EM radiation is Faraday Rotation. I strongly suspect we have a lot more these days. Amusing story. Fermi's wife had a degree in general science that did not cover...
  10. PainterGuy

    How is the wavelength of emitted EM radiation measured?

    Hi, Source: https://en.wikipedia.org/wiki/Second#"Atomic"_second How were such huge number of periods per second measured originally? Was an instrument such as Michelson interferometer used? I think it was Albert Michelson who invented the interferometer to make calculations of wavelength and...
  11. W

    The every day use of the magnetic part in EM radiation

    As I understand it, it is the magnetic part of electromagnetic radiation which creates a current (AC) in a radio receiver (i.e in an antenna) which can be translated into sound/graphics and so on. Is this correct? I mean in the sense that it is the magnetic field in the incoming radiation which...
  12. A

    EM radiation strength wrt time

    So I see EM radiation , visible spectrum including being portrayed as two sinewave vectors each perpendicular to other one being that of the E field the other being the B field, the field is carried by photons, let's take the visible spectrum as an example. So having a specific frequency the...
  13. S

    Piezoelectric Effect and EM Radiation

    It's my understanding that deforming a piezoelectric crystal causes electric charges to build up on the outer faces of the material. What I would like to know is if these charges behave like the free charges in a metal. More specifically, does deforming a piezoelectric crystal effect how em...
  14. S

    Frequency and energy of EM radiation

    Am I correct that the direct proportionality between the energy and frequency of an EM wave can be obtained from classical electromagnetism? Of course there's the Planck–Einstein relation ##E = h \nu## for a photon, but that entails QM. I'm wondering about the relation ##E \propto \nu## for an...
  15. G

    How do we visualize EM radiation?

    What is the best analogy to explain electromagnetic fields? I have seen the depictions of em radiation as perpendicular waves. Do we exist in a huge sphere of em radiation in which waves such as cell phone signals and radio broadcasts can be thought of as spherical ripples that emanate at the...
  16. P

    I EM Radiation of "Permanent" Molecular Electric Dipoles

    Suppose I were to subject a polar molecule to a high-frequency electric field. The polar molecule responds to the high-frequency electric field and thus it has a time-varying electric dipole moment vector. If we treated this as a classical electric dipole, it would be expected to radiate some of...
  17. Pushoam

    Relation between E and B of em radiation

    Homework Statement Homework EquationsThe Attempt at a Solution From the equation it is clear that the wave is propagating in y direction. So, the magnetic field is along z- axis. ……….(1) Dimensionally B = E/v……….(2) According to the above two conditions , the correct option is (c). Is this...
  18. Pushoam

    Wavelength of em radiation of H - atom

    Homework Statement Homework EquationsThe Attempt at a Solution E = (13.6 – 3.4 = 10.2)eV = ## \frac {hc } { \lambda } ## =1.22 * 10^{-5} cm So, the correct option is (a). Is this correct?
  19. Z

    Relation of EM radiation equation to radioactive decay

    Hello, I am a Mechanical Engineering student but I am a TA for an electricity and magnetism course, and I had a student ask a question that's a little bit outside my understanding. The question was related to the equation for a radiating electric field from an accelerating charged particle...
  20. Borek

    I Neutron star merge why didn't all EM radiation came at once?

    Bear with me, I am just a chemist. Observations took several days (up to two weeks if memory serves me well). What I wonder is - why had different types of the EM radiation came at different times? Gamma burst was observed at almost exactly the same time gravitational waves were detected, but...
  21. Pushoam

    Do photons emitted by charged particles in a uniform loop get canceled out?

    A clump of charged particles moving in circular motion emits em radiation. But if I go on increasing no. of charged particles till the time the system becomes current in circular path, then since each particle is having same acceleration and velocity, the current will be uniform. So, now the...
  22. Pushoam

    Variation of EM radiation with frequency

    Homework Statement X-ray pulses, visible-light pulses, and radio pulses (the latter corrected for dispersion in the interstellar plasma) emitted by an astronomical object called a “pulsar” are all observed to arrive simultaneously at the Earth — with an uncertainty of only 200 microseconds. The...
  23. H

    How could 2 crossed fields polarize and deflect EM radiation

    In the 1953 science fiction novel Childhood’s End by Arthur C. Clarke, characters use two crossed fields in outer space to block some of the solar radiation traveling towards earth: “Somehow, out in space, the light of the Sun had been polarized by two crossed fields so that no radiation could...
  24. Jim Lundquist

    Thought Experiment on the Dual Nature of EM Radiation

    The following question/thought experiment is based on the dual nature (particle/wave) of electromagnetic radiation. Consider the emisson of a single photon on a 3D grid along the x-axis with its origin at (0,0,0). The only matter in this experiment consists of “electrons” found only in...
  25. N

    B Could the opacity of a material to one band of EM radiation be altered by X-ray illumination?

    -iation. Could the opacity of a material to one band of EM radiation (light) could be altered by irradiating the material with another band of EM radiation (X rays)? I think you are suggesting that: By raising the electrons in the atoms to higher energy bands (with the X rays), so that they will...
  26. ElijahRockers

    EM radiation appearing to travel faster than C

    I just had a flashback to an applied electromagnetic course I took a few years ago. I believe we were learning possibly about waveguides (maybe) or something, but there appeared a phenomenon in the math that made it appear as if the wave was traveling faster than C. When asked about it, the...
  27. N

    Energy lost by EM radiation per cm in air?

    Hey all, is there a formula that can calculate the energy losy by a photon traveling through air at 1 atm per meter given frequency? Any help apreciated.
  28. DiracPool

    Relative strength of E and B fields in EM radiation

    I think the equation for the relationship of the E (electrical) and B (magnetic) fields in electromagnetic (EM) radiation is E=Bc, where c is the speed of light. I think this is correct, but what does it tell us? On it's face, it looks as though the B field (of a photon, say) is...
  29. Abhirikshma

    Energy dissipation in a travelling EM wave

    How is energy dissipated in a traveling electromagnetic wave ? Will there be any dissipation if it were to travel through vacuum ?
  30. S

    UV Light Penetration: Explaining Heuristic of Photopolymers

    For a photopolymer, the heuristic goes that longer wavelengths of UV light penetrate deeper than shorter wavelengths of UV light. For example, the UVA spectrum penetrates more deeply into the photopolymer than the UVC spectrum. What is the best way for this to be explained?
  31. blue_leaf77

    Hamiltonian of an electron under EM radiation

    I might have learned what I am going to ask during my electrodynamics class long time ago but just that do not remember it now. I always wonder why does an electron moving in space with EM radiation have Hamiltonian of the form ## H = \left( \mathbf{p}-e\mathbf{A}/c \right)^2/2m +e\phi## where...
  32. A

    2 Q's: EM radiation produced by positive charge

    I have 2 questions about EM radiation produced by an occilating electric charge. Q1: With graphs of electromagnetic fields, you can see that it contains an electric and magnetic component. What does these mean or give information about? Q2: By occilating the charge, you will get such a graph...
  33. O

    Pigments, EM radiation and quantum mechanics.

    An article in Wikipedia tries to explain pigments. One particular section has the following: "A wide variety of wavelengths (colors) encounter a pigment. This pigment absorbs red and green light, but reflects blue, creating the color blue." Questions arise... They may see stupid, but please...
  34. ORF

    Can we find EM radiation in charged particle's decays?

    Hello. I was taught that a charge which changes its velocity must radiate (at least, in classical electrodynamics). Let's consider a charged particle which decays into another charged particle (and, maybe, others neutral particles; but not photons). In this case, can we find electromagnetic...
  35. S

    How to increase reaction rate using EM radiation?

    I want to pump energy into a chemical species to increase its reaction cross section with another. Typically these species react upon collision when their relative kinetic energy exceeds the activation energy. I want to find a way to increase the reaction rate for interactions at slower...
  36. K

    Gravitational waves analogous to photons and EM radiation?

    Are gravitons and gravitational waves analogous to photons and EM radiation?
  37. R

    Energy Of A Single Photon In Em Radiation?

    Energy Of A "Single" Photon In Em Radiation? Is the energy of all photons in em radiation same? That is, say light differs from radio waves only in the number of photons per second
  38. R

    Can microwave em radiation interferes with radiowave em radiation?

    Just a thought because of the anomalous Planck satellite cmb data, and the second largest continuous structure in our solar system that almost fried the pioneer probe... Jupiter's magnetosphere which is known emitting radiowaves.
  39. I

    Polarizing EM radiation, how does it work?

    for RF, how does this mechanism work? http://i.imgur.com/Crx4Amx.png how does the conductor do this? and why does the unpolarized RF not seep through the spaces between the conductive bars?
  40. Barnak

    Angular momentum loss from quadrupole EM radiation

    I'm looking for the general formula for Angular Momentum radiated away from quadrupolar electromagnetic radiation. I searched the usual books (Jackson, Landau-Lifchitz, ...) and just found the usual dipolar contributions. Using dimensional analysis and energy radiated away, I found this...
  41. Z

    Phase velocity of EM radiation in free space

    Homework Statement (i) What is the phase velocity of EM radiation in free space? (ii) What is its group velocity? Homework Equations The Attempt at a Solution Using the definition as per this page: http://physicsdaily.com/physics/Phase_velocity (i) Vp = (C^2)/Vg (ii)...
  42. N

    What's the source of EM radiation

    An electron and a positron annihilate and energy is released in the form of quantized EM (gamma etc.) rays: Now some childish yet inquisitive questions; 1. Where were there quanta prior to annihilation, inside the electron or positron (or both)? 2. Were these quanta really present...
  43. dbmorpher

    What is the Height of EM Radiation

    Hello, I have always wondered, what the relation of wavelength and frequency to the amplitude is. Is there an equation? Does it vary with different types of waves? Can it change?
  44. shounakbhatta

    Pulsars - Rotating neutron star produces EM radiation?

    Pulsars -- Rotating neutron star produces EM radiation? Hello, If a neutron star is composed of neutrons, which do not carry any electric charge then how it's rotation produces pulsars which are electromagnetic radiation? Thanks.
  45. Q

    Detecting visible light EM radiation with an antenna

    If visible light is part of the EM spectrum just like radio waves, is it possible to construct a radio like antenna (metal pronged structure) to detect them?
  46. S

    Finding the minimas from EM radiation.

    Homework Statement 6. S1 and S2 in the diagram are effective point sources of radiation, excited by the same oscillator. They are coherent and in phase with each other. Placed 4.0 y m apart, they emit equal amounts of power in the form of 1.0 m wavelength electromagnetic waves. (a) Find...
  47. N

    Advanced EM Radiation Books: Info on Velocity EM Field

    Hi ,does anyone know a good book in advanced EM radiation and it contains more information on velocity EM field , I have already finished Griffith's book
  48. A

    Relationship between EM Radiation Energy and Electric/Magnetic Field Magnitude

    the energy of em radiation (or photon) is proportional to the frequency of the radiation. the em radiation (or photon) is composed of oscillating Electric and Magnetic fields. as such this energy must be stored in the oscillating electric and magnetic fields constituting the radiation...
  49. E

    How are stellar EM radiation formed?

    How are stellar EM radiation formed?? I've read this in many books and sites... Any object above 0 K will emit EM radiation of all wavelengths... Now this is confusing me a lot... I mean, how for example a sun emit wavelength s of a Radio and it is the same sun which emits ultra violet and...