What is Electromagnetic waves: Definition and 329 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. deuteron

    I Why don't we talk about the E & H fields instead of E & B fields?

    We have the following constitutive relations: $$ \vec D= \epsilon_0 \vec E +\vec P$$ $$\vec B=\mu_0\vec H + \vec M$$ And Maxwell's equations are: $$\nabla\cdot\vec D = \rho$$ $$\nabla\cdot \vec B=0$$ $$\nabla\times\vec E=-\frac{\partial\vec B}{\partial t}$$ $$\nabla\times\vec H=\vec j...
  2. D

    I How to Measure the Energy of an Electromagnetic Wave?

    We know a way of measuring energy of a electromagnetic wave is the Poynting vector, which is independent of the frequency. But let's say we want to make two different electromagnetic waves, with different wavelengths and so different frequency, but with the same amplitude (so same Poynting...
  3. A

    B Doppler effect on electromagnetic waves in a car

    Is the doppler effect on electromagnetic waves receive by cell phone in fast car and so somebody talk with cell phone in fast car view this effect
  4. M

    I Constructive interference of harmonic electromagnetic waves

    Hello ! I have a doubt as to how is this case, if it occurs, of the constructive interference of two harmonic electromagnetic waves but of different wavelengths or frequencies between them. That is, if between the two electromagnetic waves a new and unique electromagnetic wave is created and...
  5. M

    I Energy of Electromagnetic Waves in Destructive Interference

    Hello ! As we know by definition that: "Constructive interference occurs when the phase difference between the waves is an even multiple of π (180°), whereas destructive interference occurs when the difference is an odd multiple of π." But my question is in the case of destructive...
  6. A

    I Gravitational vs. Electromagnetic Waves: What's the Difference?

    in a nutshell what are the differences between gravitational and electromagnetic waves?
  7. G

    B Can electromagnetic waves traverse wormholes?

    Hello I'm new to this forum and interested in astrophysics and metaphysics. My first question here is if we can create nano sized wormholes to send information faster than light to other stars for example. We don't need to travel if we could send small satellites or even just radiowaves to the...
  8. H

    I Group velocity for an electromagnetic wave inside glass

    Hi, I saw that the group velocity for an electromagnetic wave can be calculate with the following formula ##v_g = v_p + k \frac{d v_p}{dk}## Thus, since ##v_p = \frac{c}{n} = \frac{\omega}{k}## Is it correct to say that ##v_g = \frac{c}{n} + k(- \frac{\omega}{k^2})## where ##k =...
  9. samy4408

    B Question about electromagnetic waves -- Penetration vs. Frequency

    I read in a book that high frequency electromagnetic waves are more able to penetrate than low ones , so why radio waves can penetrate walls when light cannot?
  10. Andreea007

    I Defining electromagnetic waves

    Hi! So I'm trying to understand electromagnetic waves but I encountered different definitions: one in terms of electrons and one in terms of photons. Which ones are actually used to produce electromagnetic waves and how? Also, I saw that alternating current generates electro magnetic waves, but...
  11. M

    I Gravitational Field of Electromagnetic Waves: How is it Generated?

    Hi ! It catches my attention that atomic particles such as protons, neutornes, electrons and their respective subparticles such as Quarks are theoretically formed by high-energy electromagnetic fields such as gamma rays and then the gravitational field that would generate the mass of these...
  12. Dom Tesilbirth

    The resultant intensity of two interfering waves

    My Try: The resultant field is given by $$\begin{aligned}\overrightarrow{E}=\overrightarrow{E}_{1}+\overrightarrow{E}_{2}=\widehat{i} E_{0}\cos \omega t+\widehat{j}E_{0}\cos \left( \omega t+\phi \right) \\ \Rightarrow E^{2}=E_{0}^{2}\cos ^{2}\omega t+E_{0}^{2}\cos ^{2}\left( \omega t+\phi...
  13. O

    I Momentum in electromagnetic waves

    Hi all! These days I am brushing up my knowledge on EM Waves. I begin with the introductory level but I don't mind to engage in an advanced treatment of the topic. At the very basic level I had a high school book, the mentions straightway that if the wave carries with it an energy U, it posses...
  14. greg_rack

    Parameters and the nature of electromagnetic waves

    By rearranging over and over ratio formulas involving frequency, speed and wavelength, I came up with the equation: fP/fQ=10^-8xVP/VQ This led me to take into account only rows A, B, E, and F... but I can't really understand which one of these is the right one.
  15. Adesh

    Derivation of [itex] p = \frac{E}{c} [/itex] using Maxwell's light

    Imagine that we have an electromagnetic wave or light propagating in x direction, and \mathbf{E} is oscillating in z direction and \mathbf{B} in y direction. The picture looks something like this Now, if there exists a charged particle q on the xx axis at rest, then our B field can't do...
  16. A

    Do plants respond to low frequency electromagnetic waves?

    I'm wondering if plants are sensitive to electromagnetic (EM) waves? Of course I'm not speaking of light but in the low frequency domain, say from 0 Hz to 100 kHz? I looked up the web but couldn't find anything, only experiments with EM waves above the range of 300 Mhz. Has there been any...
  17. ContagiousKnowledge

    Electromagnetic waves incident on an anti-reflective coating

    We're trying to prove this: There exists 3 distinct regions: Region 1 has index of refraction 1 and lies before light hits the coating. For simplicity, define the position of the interface between the air and the coating z=0. The second region is the coating, which has index of refraction √n. At...
  18. D

    Electromagnetic waves radiating away from a transmitting tower

    Homework Statement: A radio station on the surface of the Earth radiates a sinusoidal wave with an average total power of 50 kw. Assuming that the transmitter radiates equally in all the directions above the ground, at a distance of 100 km from the antenna (ε0 = 8.85 10-12 C2N-1m-2) Homework...
  19. GuillemVS

    Electromagnetic Waves and different energy manifestations

    When an object is hot its particles are moving faster than when is cold, right? I've searched that particles are electrons and protons, so it means that if we warm a object the electrons will be moving or even accelerating. Every charge accelerated creates Electromagnetic Waves (or light)...
  20. Sophrosyne

    Electromagnetic waves in charged/magnetic fields

    Electromagnetic waves are oscillations of the electrical/magnetic field which propogate through space. So one might predict that the presence of a magnet/charged particle would effect their propogation somehow, like distortion or interference (eg, light might get refracted in a magnetic field or...
  21. J

    I Are electromagnetic waves sine waves?

    Light is said to consist of photons or electromagnetic waves. I'm not asking which view is correct, what conditions make one view or the other more useful, or advantages and disadvantages of each view. I am assuming the two views are compatible to the extent that the wave character of light can...
  22. R

    Do electromagnetic waves moving upside down change?

    do electricmagnetic wave moving in upside down form? So the highest position is wave crest and the lowest is wave trough?
  23. A

    What are the most intense electromagnetic waves in nature?

    Basically as the title says. I'm interested in the naturally occurring EM waves, and I would like to know the strongest EM waves out there. I'm not talking about "strong" as in energy per photon that is proportional to the frequency, but about the overall energy transported by the wave that is...
  24. Samuel Gosselin

    Which electromagnetic waves does a source emit?

    If a source emits high frequency electromagnetic wave, for example gamma rays, does it imply that it also emits all the waves of lesser frequency?
  25. B

    Problem about electromagnetic waves -- Writing equations for B(t) and E(t)

    Hi! I'm trying to solve a problem and I'm lost. Would someone kindly help me with the solution, please? 1. Homework Statement A plain electromagnetic wave with a 20GHz frequency moves in the positive direction of the Y axis and its magnetic field is oriented along the Z axis. The amplitude of...
  26. F

    Electromagnetic waves: How broad is a plane wave?

    Hello all again, I was just thinking again about another aspect of electromagnetic waves: Assume we have a planar wave. How "broad" is it or how far does the electric field of it reach? For instance if we have a single planar wave, assume the k-vector in the direction of propagation and then the...
  27. F

    Electromagnetic waves: Photons generated by two charges attracted to each other?

    Hello all, after thinking about properties of electromagnetic waves, especially concerning the electric field of them, I ran into some serious understanding problems: 1) photons are electromagnetic waves and vice versa and they convey electrical force. Let's now do a thought experiment: let's...
  28. M

    How do we know electromagnetic waves are light?

    Per the maxwell equations, we know that em waves travel at the velocity of light, but that is not a sufficient condition to say that electromagnetic waves are light. How do we know that electromagnetic waves are light? They could just be something that has the same velocity as light. Any...
  29. M

    Electromagnetic waves from a dipole antenna

    Hello, I've been reading up on this topic and have a couple of questions. This videos shows what I am referring to: 1. What makes the electromagnetic waves from a dipol antenna spread out? There would have to be some type of force that pushed them outwards, right? 2. When the electromagnetic...
  30. Cathr

    Electromagnetic wave equation - phase and amplitude

    There are some things that confuse me about electromagnetic waves, and I haven't found good answers anywhere. Consider the following equation: E=E0 e i(wt-kx) (here E and E0 are vectors, I couldn't find the right symbols). The things that confuse me are the following: 1° We say that the power...
  31. F

    Electromagnetic Waves: Static Charges & Relativity Predictions

    I have learned about the electric fields of static charges and those of moving charges. From what I gather(although I have not really learned the specifics) when charges are accelerated they emit electromagntic waves which are essentialy an electromagnetic field progagating through space. My...
  32. A

    Electromagnetic Waves — Given E, find B....

    Homework Statement A plane electromagnetic wave travels upward. At t = 0, x = 0, its electric field has the value E = 5 V/m and points eastward. What is the wave's magnetic field at t = 0, x = 0? Homework Equations B=B init. sin(kx-wt) E=E inti. sin(kx-wt) E=cB The Attempt at a Solution I am...
  33. M

    Understanding an electron's emission of electromagnetic waves

    Hi to everybody ! I was thinking about something which confuses me about wave emission. The question is simply the following: Does an electron emit light when it accelerate? or just during its deceleration? or maybe when acceleration and deceleration alternates in some order? I'm not really...
  34. A

    Do electromagnetic waves have potential and kinetic energy

    Do electromagnetic waves have potential and kinetic energy like springs, strings, etc. If so how are they calculated, inter-related? What is the total energy? Are the energies fluctuating over time? I am a physics hobbyist so generally the first answers should come with the least mathematics...
  35. Y

    Electromagnetic waves and other waves

    Hello everybody, I am new here :) what exactly is the energy of the wave? how to think about it generally, in electromagnetic waves and in relation to amplitude? I can think about the kinetic or potential energy that a particle can get from that kind of wave or the sum of all such energy in all...
  36. P

    An Electromagnetic wave goes from air into a medium....

    Homework Statement An EM wave from air enters a medium. The electric fields are --> ^ E1 = E01 cos(2πv(z/c-t) x --> ^ E2 =E02cos(k(2z-ct)x in a medium ,where the wave number k and frequency v refer to their value in air.the medium...
  37. C

    How an oscillator creates electromagnetic waves

    Homework Statement A cell phone sends and receives electromagnetic waves in the microwave frequency range. Explain the physics of how an oscillator creates these waves. Homework Equations n/a The Attempt at a Solution An electromagnetic wave is created by the functioning of the oscillator...
  38. M

    How long can electromagnetic waves last?

    Hello, I am reading a book on the history of the universe. The book says that we can still detect the electromagnetic waves generated at the big bang in the form of white noise. I am not sure how it works, because the waves transmitted by AM or FM radio antennas die down after propagating some...
  39. I

    Two States of Polarization of EM Waves

    I am studying about the cavity radiation inside a metallic cube. In the textbook it states that there are two independent waves corresponding to the two possible states of polarization of electromagnetic waves. What does it mean by this? (My current assumption is the phase change of the waves)...
  40. C

    Can an axisymmetric electric field be created without charges?

    That is, a field that accelerates charges in opposite directions on each side of an axis. I was thinking about interference of similarly polarized waves traveling in opposite directions (so that electric field peaks and valleys overlap but magnetic field adds constructively) - would there be an...
  41. E

    Radio waves interaction with other electromagnetic waves

    when it is asked that why radio waves do not interact with the magnetic field of electric wires or magnets, people say that radio waves are not "matter" and they do not have "charge". i really can not understand this for ex think about 2 magnets. The magnet A has a magnetic field and when we put...
  42. L

    How to determine the direction of the E-field of an EM wave

    Homework Statement Consider a wave vector which hits a plain boundary between water and air. The wave vector hits the boundary with an angle α1 measured from the vertical axis. The magnetic field amplitude has a y-component only. Also, notice: The z-axis is the horizontal axis, the x-axis is...
  43. C

    I If electromagnetic waves propagate, do photons as well?

    In classical physics, EM waves propagate this is one of the main features of all waves in general. Usually for mechanical waves the elements (like molecules) that vibrate do some little motion. For example a string can move up and down, but the waves travel further through propagation. The...
  44. C

    I Relativistic Field Transformations and EM Waves

    If we move towards a source of EM waves, in our reference frame the frequency appears (and it is) higher than what a stationary observer will see due to Doppler effect. The field transformations show that these two observers will se static fields differently so I would also expect that the peak...
  45. A

    How is Light (electromagnetic waves) generated by electrons

    I know this question might be too simplified but, What is the primary causes generation of light (electromagnetic waves) by electron? Is it vibration motion of electron or the motion of electron around the nucleus?
  46. Pushoam

    Range of frequency of electromagnetic waves

    Theoretically speaking, does the frequency of em wave range from 0 to infinity?
  47. Vaibhav Sahu

    Propagation of EM Waves in metamaterials

    We have materials that have negative effective permittivity and permeability. In such materials, when the product of permittivity and permeability is negative, solving the wave equation yields a wave with a purely imaginary wave number. Does this mean complete attenuation of the wave ?
  48. S

    Difference between probability waves & electromagnetic waves?

    What I know: A ripple/wave in a field gives rise to a particle. For example, a ripple in electric field creates a photon. Question: Is this the same principle as probability wave which when observed reveals a particle?
  49. 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...