What is Electromagnetic radiation: Definition and 161 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. asf33

    I Electromagnetic radiation, photons, quantized energy levels

    Hello! Im a freshman in college, taking pretty basic chem classes and Ive found myself in a deep dive regarding quantum physics. Im sure this is pretty simple and easy compared to everyone else on here but I feel like I keep getting oversimplified answers that just leave me with more...
  2. cemtu

    I Why is bremsstrahlung radiation greater than acceleration radiation?

    Why is breaking radiation stronger than accelerating radiation? Why is it that when an electron comes accelerating toward a nucleus radiate weaker than when it goes decelerating away from the nucleus? Is it because when it decelerates, at the same time it changes direction? Or is it because it...
  3. P

    I Colorless Compounds and electromagnetic radiation

    I was trying to understand why some compounds appear colorless (transparent) and tried to give an explanation. I take benzene as an example: it is a chromophore group in which there is π-conjugation, so a certain energy gap is generated between HOMO and LUMO. This energy gap is such that in...
  4. S

    I Brownian motion of charged particles?

    If we have charged particles having Brownian motion, would this motion be associated with (or produce) heat or electricity? Would it produce electromagnetic radiation (and if it would produce it, what type of radiation in the electromagnetic spectrum)? Could there be Brownian motion of charged...
  5. J

    I Cosmic Inflation Explained: Constant Velocity of Electromagnetic Radiation

    C = sqrt(E/M)...this would suppose the ratio of the amount of energy vs. the amount of mass in the universe. If not, why not. If there is no mass, just energy, or much less mass at the moment of the hypothetical Big Bang, then, there C would be significantly higher, thus explaining cosmic...
  6. Salmone

    I Derivative of the retarded vector potential

    In a problem of an oscillating electric dipole, under appropriate conditions, one can find, for the potential vector calculated at the point ##\vec{r}##, the expression ##\vec{A}=\hat{k}\frac{\mu_0I_0d}{4\pi}\frac{cos(\omega(t-r/c))}{r}## where: ##\hat{k}## is the direction of the ##z-axis##...
  7. Salmone

    I Something about retarded potentials for oscillating electric dipole

    In a problem of an oscillating electric dipole, under appropriate conditions, one can find, for the potential vector calculated at the point ##\vec{r}##, the expression ##\vec{A}=\hat{k}\frac{\mu_0I_0d}{4\pi}\frac{cos(\omega(t-r/c))}{r}## where: ##\hat{k}## is the direction of the ##z-axis##...
  8. K

    B "Prove" that LPG burns with a blue flame ....

    The household LPG burns with a blue flame. There's nothing to prove! But what if we attempt to do that? How do we go about it? I started with the assumption that it is a complete combustion of the LPG. A Google search tells me that the calorific value (the amount of heat a substance gives off...
  9. Homestar1

    Electromagnetic radiation (EMR) threshold

    What is the threshold energy (or frequency) required for an electromagnetic field to transition from a near field to become self propagating (EMR), far field? (If I'm using the right definitions to ask the question correctly). Is this constant or are there other details needed to calculate this?
  10. Mr_Allod

    EM Wave Reflection and Transmission Between 3 Materials

    Hello there. I set up the problem like this, I have a wave incident from air on the anti-reflective coating consisting of: ##\tilde {\vec E_I} (z,t) = \tilde E_{0_I} e^{i(k_1z- \omega t)} \hat x## ##\tilde {\vec B_I} (z,t) = \frac 1 v \tilde E_{0_I} e^{i(k_1z- \omega t)} \hat y## This wave gets...
  11. F

    Teaching about electromagnetic radiation & struggling

    Summary:: I teach high school (grade 12) and have always struggled with teaching about electromagnetic radiation. I'm looking for resources aimed at laypeople about EMR that may give me some ideas on how to teach it more clearly. I teach high school (grade 12). We have just finished a unit...
  12. Amathproblem22

    MHB Electromagnetic Radiation and Health

    Well, the title pretty much sums up my question. I want to know about electromagnetic radiation and the effects on human health in your opinions and knowledge! I have done research into the topic and also gone down the road of things like wifi(modern technology) effects on health and most...
  13. J

    Estimation of the power in a received radio signal

    I would like to estimate the magnitude of a radio signal received from a transmitter by first principles: Transmitter antenna length ##L=1## m Transmitter antenna area ##A=1\hbox{ cm}^2## Number of electrons per unit volume in antenna ##n_e=10^{28}## Radiation resistance of antenna ##R_R=10\...
  14. J

    Electromagnetic radiation effect on health.

    Some site I've looked at are https://www.sciencedaily.com/releases/2000/10/001016073704.htm and [Link to garbage site removed]
  15. T

    I Electromagnetic Radiation in Strong Gravity Field

    Does the electric and magnetic fields of electromagnetic radiation remain perpendicular in the presence of an intense gravity field? If not, what is the physical ramifications of this?
  16. O

    Electromagnetic radiation measurements

    What does a measure of 2000 µW/m² electromagnetic radiation by "Hf35c Rf Analyze (800mhz – 2.5 Ghz)" radiation meter mean? Is it too high? see this link: https://www.electrahealth.com/hf35c-radio-frequency-meter.html it shows that “1000 or more µW/m²” in the meter is “Extreme Concern”, does it...
  17. D

    How short can electromagnetic radiation become? Shorter than gamma rays?

    is there some physical limit on the wavelength of electromagnetic radiation? Can there be radiation shorter than gamma rays?
  18. R

    B Absorption of electromagnetic radiation

    Hi, I wonder why with electromagnetic radiation, there's some radiation that penetrates with Earth atmosphere such as visible light, while other can't like gamma radiation. What does the penetration of any em radiation on any object depends on
  19. Lukeblackhill

    Heat during the Day: Answers to Your Questions

    Hi! My question is: I understand that at noon-day it’s hotter because of the angle with which sun rays enter our atmosphere. But at the same time, I was wondering that the band of radiation responsible for heating things is infrared, and that at noon basically all bands of lower frequency than...
  20. T

    Electromagnetic Radiation Emitted By An Accelerating Charge

    Suppose a point charge is slowly oscillating simple harmonically. Does it emit an electromagnet wave and if not why not ? How does its field change with time. Does anyone know of a good animation ? Thanks.
  21. S

    Does electromagnetic radiation react with antimatter?

    And if it does what is the mechanism and can it be used in astronomical spectroscopy?
  22. D

    Accelerating charged particles and conservation of energy

    Hi I'm wondering how when a charged particle is accelerating it both emits energy in the form of em radiation while also gaining kinetic energy. All of that energy comes from the thing accelerating the charged particle, yeah? Is that necessary, like it is not possible to give a charged particle...
  23. C

    I Calculate the Efficiency of a Winston Cone

    How can I calculate radiation transfer efficiency of a Winston cone, assuming a constant efficiency for every reflection at 99% and that the source is perfectly diffuse and covers completely the wider entrance of the cone? Also, are there more efficient non-imaging radiation concentrators with...
  24. enter

    I What is the highest frequency of electromagnetic radiation?

    Title says it all. Also, if the frequency of electromagnetic radiation is limited, why? My guess is the wavelength is limited to the Planck length, and when I plug those numbers into the calculator, I get 1.855 * 10^43 Hz. The maximum (Edit: observed) frequency of a gamma ray is 3 * 10^20 Hz...
  25. MattIverson

    Electromagnetic Radiation of Single frequency Incident on a Slab

    Homework Statement The problem is state in the attachment. Homework Equations None to add. 3. The Attempt at a Solution Struggling with this problem because of the phasor part of it. Perhaps this is justified because the angle is very small and so that relates to a low frequency? Is it...
  26. E

    Gauss' Law for electromagnetic radiation?

    For the proof I've read that verifies transverse electromagnetic waves are consistent with Gauss' Law, there seems to be the suggestion that the magnetic and electric field at a given small length c(dt), along which the waves travel, propagate infinitely backwards and forwards in their...
  27. J

    Electromagnetic field disturbance if radiation disappears

    Hi everyone! I've been reading about these topics (Feynman lectures and more on the internet and some books) but I still have a doubt, maybe because I haven't understood the whole of it. This is my doubt: Think of an imaginary situation in which we have an accelerating charge. The...
  28. G

    Is Faraday Cage able to stop all electromagnetic radiations?

    I'm trying to understand if it does exist something (material, construction) that shiled you against alll kind of electromagnetic radiations. Something that shields you from the lowest frequency radio waves up to the highest frequency gamma rays. I've read about faraday cage but it does not...
  29. J

    Estimating Electromagnetic Radiation from a Cellular Phone

    Hello all, I have a problem with a typical style of problem I seem to always struggle with. Just to clear this up, I am studying for my comprehensive exams later this summer. So I am going through past problems to bone up on the last two years of grad school. At which point I came across this...
  30. Ian Baughman

    Understanding Electromagnetic Waves

    So I know that EM waves travel perpendicular to the electric and magnetic fields which are also perpendicular to each other. What I'm having difficulty understanding is since light is an EM wave and can travel through the vacuum of space, does that imply that everywhere in the universe there is...
  31. Samama Fahim

    Spectral Intensity as a Function of Wavelength in Blackbody Radiation

    A blackbody is also a perfect emitter giving off electromagnetic waves at all frequencies. A detector could measure the intensity of the radiation it receives through the prism. By moving the detector to different positions, you could measure the intensity of light as a function of color or...
  32. G

    Classical and quantum interpretations of electromagnetic radiation

    Hi, So I can get the idea that the ac current in a radio transmitter produces radio waves of the same frequency of the ac supply, just like shaking a slinky sprung up and down but how does this translate into the radio waves as actually coming out as photons and for that matter other than...
  33. D

    Electromagnetic Radiation temperature

    Is there a meaningful way to convert the energy of an electromagnetic wave to a temperature? I mean this more along the lines of how the universe has a temperature of 2.7 kelvin due to electromagnetic radiation. I'm honestly just curious to determine the temperature of the universe after nearly...
  34. Vitani11

    What happens to electromagnetic radiation during collision?

    Homework Statement When a particle is accelerated toward another particle it is giving off electromagnetic radiation in the form of gamma waves. After a particle is annihilated, pions are transferred between the particles which turn into gamma waves which decay into (for example) an electron...
  35. T

    I need to prove a superhero.

    Hi! For project in one of my classes, I have to research a super power and a possible scientific explanation of it, showing either why it can or can't happen. I chose a super power of translating people's electro magnetic fields into frequencies, and being able to translate that into...
  36. J

    B Gravity and electromagnetic radiation

    Do falling charged particles radiate? Also, if I hold a charge still and bring a large mass close to it first on one side then another so that the particle sees a sinosoidally oscilating gravitational field will it radiate?
  37. 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...
  38. D

    Electromagnetic radiation effect on electric field?

    Hi, just trying to better understand this concept of electromagnetic radiation. My understanding thus far is that it is a traveling disturbance in the electric field. This picture here seems to help me see what is happening...
  39. Green dwarf

    Is electromagnetic radiation a form of kinetic energy?

    Hi, I'm a high school science teacher. Most textbooks classify EM radiation as kinetic energy. But this doesn't seem right to me. As a photon is massless it's hard to see how it can have kinetic energy which is 1/2 mv^2. It could be said that it has energy hf and therefore mass hf/c^2. Then its...
  40. afcsimoes

    B Is there a minimum wavelength for electromagnetic radiation?

    The wavelength is inversely proportional to the foton energy. So, the limit can be stated by the mass of the full universe. But how much near that limit can the light be?
  41. N

    B Can we know what exists in planets' subsurfaces?

    imagine this situation: there's a very similar planet to Earth with almost the same atmosphere and surface. we want to know what lies beyond the surface to know if life exists there. so could we send or observe radio waves or microwaves with a similar telescope as arecibo that penetrates several...
  42. P

    Antennas and electromagnetic radiation

    Antennas work with variable current that leads to accelerations and deceleration ofor the electrons, the frequency of the photon or the electromagnetic radiation I want to generate depends on the change in kinetic energy of the electron E= hf= change of kinetic energy of the electron, according...
  43. Hongo

    I Radio Comm Between 2 Points Diff Gravity: True?

    A source that is orbiting close to a singularity of a black hole is transmitting a radio frequency signal that lasts 60 seconds and is repeated infinitely. The signal is being transmitted using the amplitude modulation method (AM Radio). Let suppose that each minute passing in the transmitting...
  44. TheSodesa

    Two linear polarizers in series

    Homework Statement The optical power of a HeNe -laser is ##P_0 = 5.0mW## and the wavelength ##\lambda = 633nm##. The emitted light is linearly polarized. As the laser beam travels through two in-series -polarizers, the power detected behind the second polarizer ##P_2 = 1mW## . If the first...
  45. B

    Speed of electromagnetic radiation

    Does electromagnetic radiation emitted by cold hydrogen gas travel at the speed of light?
  46. S

    Electromagnetic radiation pressure

    I am confused with the fact of radiation pressure on Wiki and my homework solution. They are both arguing that the pressure produced by a ray of light to be reflected with incident angle θ and intensity I is: $$\frac{2I\cos^2(\theta)}{c}$$ My thinking We know that: $$Ft=\Delta p$$ We see the...
  47. marciokoko

    Electromagnetic radiation vs Capacitance and Inductance

    Im trying to compare, visually in my head, the difference between transmitting data vs something like radio or microwaves vs how inductance and capacitance. I understand that the way the wave is modulated for example, AM or FM, can be interpreted as 0s or 1s. Im trying to compare this to...
  48. J

    Evanescent light waves, energy flow and tunneling

    In the full internal reflection case where we have a refracted evanescent wave, If another object is nearby, then we could have wave tunneling phenomenon(frustrated total internal reflection). 1) So, how can the evanescent wave which does not transfer any net energy produce another wave at the...
  49. E

    What is the intensity of an electromagnetic radiation?

    How can I compute the intensity of an electromagnetic radiation if I know ##e_x, e_y, e_z, h_x, h_y,## and ##h_z##, where ##e_i## is the electric field component at ##i## and ##h_i## is the magnetic field component, also at ##i##? Thank you in advance.