What is Electromagnetic: Definition and 1000 Discussions

Electromagnetism is a branch of physics involving the study of the electromagnetic force, a type of physical interaction that occurs between electrically charged particles. The electromagnetic force is carried by electromagnetic fields composed of electric fields and magnetic fields, and it is responsible for electromagnetic radiation such as light. It is one of the four fundamental interactions (commonly called forces) in nature, together with the strong interaction, the weak interaction, and gravitation. At high energy, the weak force and electromagnetic force are unified as a single electroweak force.

Electromagnetic phenomena are defined in terms of the electromagnetic force, sometimes called the Lorentz force, which includes both electricity and magnetism as different manifestations of the same phenomenon. The electromagnetic force plays a major role in determining the internal properties of most objects encountered in daily life. The electromagnetic attraction between atomic nuclei and their orbital electrons holds atoms together. Electromagnetic forces are responsible for the chemical bonds between atoms which create molecules, and intermolecular forces. The electromagnetic force governs all chemical processes, which arise from interactions between the electrons of neighboring atoms. Electromagnetism is very widely used in modern technology, and electromagnetic theory is the basis of electric power engineering and electronics including digital technology.
There are numerous mathematical descriptions of the electromagnetic field. Most prominently, Maxwell's equations describe how electric and magnetic fields are generated and altered by each other and by charges and currents.
The theoretical implications of electromagnetism, particularly the establishment of the speed of light based on properties of the "medium" of propagation (permeability and permittivity), led to the development of special relativity by Albert Einstein in 1905.

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  1. bcrowell

    Classical Electromagnetic Field Theory by Bo Thide

    Author: Bo Thide Title: Electromagnetic Field Theory Download Link: http://www.plasma.uu.se/CED/Book/ Prerequisities: Contents:
  2. J

    Temperature & Electromagnetic Radiation: Feynman's Perspective

    Since temperature is no more than vibrating atoms (in Feynman's words), wouldn't that induce a changing electric field, just very slow in some cases? If so, is everything that is not 0 degrees kelvin radiating some kind of EM radiation? Like an ice cube, does it radiate small amounts of radio...
  3. T

    Electromagnetic Generator Coil Number Help

    Hello, I am building a generator for a project in my physics class. I have lots of magnetic wire and 6 VERY strong neodymium magnets, their area isn't overly large (I'd say about 1.5x1.5 inches). How many coils would be best for me to make for the stator? I am making a circular spinning disk...
  4. A

    Conceptual difficulty with Electromagnetic induction

    Hi all, I have a conceptual difficulty with the idea of induction of a current in a wire due to a changing magnetic field. Initially I was very comfortable with the idea. Upon seeing the typical setup of a square wire being rotated in a region of uniform magnetic field, I was happy to accept...
  5. Islam Hassan

    Electric Field vs Electromagnetic Field

    If we have a static electric charge, it generates an electric field. If that static electric charge is accelerating, it generates an electromagnetic field. What about if the electric charge is moving with uniform velocity? Is the field thus generated an electic field or an electromagnetic...
  6. Q

    Feynman Diagram for Electron-Proton Attraction

    Would it just be the same as with two electrons? (or any other pair of particles with the same charge) I'm kinda in two minds, I suspect that is wrong because wouldn't the fact that they attract each other (instead of repelling) means that the diagram would be drawn differently?
  7. H

    Calculate electromagnetic force on iron object

    Hello, I need to calculate/estimate the force between a solenoid electromagnet and a piece of iron on a certain distance from the magnets airgap, preferable in a simple way under ideal conditions rather than a very exact calculation. I have found the following formula at a couple of places...
  8. W

    Electromagnetic levitation Relations

    Hello everyone i bought a kit for my senior project on electromagnetic levitation. It uses an electromagnet to suspend a magnet via force of attraction. It is stable because of two hall effect sensors and voltage regulator. The kit can make the magnet move in a sinusoidal and tangential motion...
  9. D

    Accelerating electromagnetic system

    Here is a picture of a situation I thought of: The circles between the magnets indicate a wire with current flowing in the direction given. This picture is a cross section of a loop of wire, looking down. Not included in this picture is the battery and non-conductive connecting materials...
  10. H

    Difference between electricity and electromagnetic waves

    Hello, Is there any difference between 50/60 AC current and a 50/60 Hz photon stream/electromagnetic wave propagating through a medium ?? Regards, Hex
  11. S

    Electrons in electromagnetic induction

    Hello, when a coil rotates in a magnetic field an AC is produced at the ends of the coil but do that electrons come from the coil wire ? If yes, shouldn't the coil run out of electrons after some time ? thank you
  12. E

    Energy transfer in electromagnetic induction

    Consider a magnet moving towards a coil. We know that the motion of the magnet will induce a current in the coil and the direction of this induced current is to oppose the motion of the magnet. Now does the magnet experience resistance to its motion immediately as soon as it starts...
  13. 2

    Electromagnetic motor using battery and magnet?

    I've been wondering how does this motor work (if it is not hoax in the first place) I was thinking about Ampere's force but apparently it doesn't really have an affect here. Any ideas?
  14. umair20

    How friction is an electromagnetic force?

    how friction is an electromagnetic force?
  15. S

    Modify crystallization process by electromagnetic fields?

    Has anyone come across an example where electromagnetic fields have been applied during crystallization processes. For example to modify crystal properties like magnetization or to change the polymorphism. In principle the use of electric / magnetic fields should change the formation of a...
  16. B

    Photon is electromagnetic field, right?

    This thread is to move this discussion away from another thread in order to talk about it in more detail, so here is a brief recapitulation of how that went to make an opening for the discussion... A photon is quanta of electromagnetic radiation, and despite the name, despite there are, I...
  17. A

    Electromagnetic induction between 2 coils problem.

    We know that 1)a change in current and voltage in a coil may result in induction in other stationary coil..this induction is directly related to frequency..ie The higher the frequency the more intense the induction effect. 2)we also know that there is no induction in case of DC current flow...
  18. J

    How do Planets generate electromagnetic waves?

    We can determine what kind of elements exist in different planets by observing electromagnetic waves from planets' direction, but does anyone have any suggestion on how planets generate electromagnetic waves at the first place? Does anyone have any suggestions? Thanks in advance for any...
  19. B

    ElectroMagnetic Wave In Liquid Help with Index of Refraction?

    ElectroMagnetic Wave In Liquid.. Help with Index of Refraction?? Homework Statement Consider the propagation of an electromagnetic wave in some liquid. The y-component of its electric field is given by Ey(x,t)=4.3 x104 V/m sin(5.40E-2m-1x + 6.00E+0 x106 s-1 t). How large is the index of...
  20. E

    Im so confused about electromagnetic induction. Need help please?

    I first thought that electromagnetic induction disobeyed the law of conservation of energy since there is another current created by another current by changing it (AC). but then there is Lenz law that says when you have yourself an current and also a changing magnetic flux, there will be an...
  21. S

    Electromagnetic Radiation Theory & Math Questions help please

    Homework Statement 1. Explain the effects To the photocurrent as the light intensity increases To the photocurrent as the frequency of the light is increased To the speed of the photoelectrons as the radiation intensity increases To the speed of the photelectrons as the radiation...
  22. N

    Polarization of Electromagnetic wave

    Dear friends i know that a wave is linearly polarized if its components have a phase difference of n*∏ and is circularly polarized if phase difference is n*∏/2. But what if phase difference is neither ∏ nor ∏/2? like for E= ax exp(-j(βy-∏/4)) + azexp(-j(βy-∏/2))... thanks in advance...
  23. W

    Measures of the intensity of electromagnetic radiation

    I've always struggled with the commonly used measures of the intensity of electromagnetic radiation and it's catching up to me lately. Suppose \bar{P}(R,\phi,\theta) is the Poynting vector of an electromagnetic field (in spherical coordinates) with norm...
  24. J

    The electromagnetic field in an accelerated frame

    Imagine a stationary charge q located on the positive y-axis at a distance r from a stationary observer at the origin. Let us assume that the distance r is large enough such that the electrostatic field due to the charge is negligible at the origin. Now let us assume that the charge q is given...
  25. P

    Electromagnetic spin from Noether theorem and spin photon

    hi, I try to use the Noether theorem to determinate the angular momentum of the electromagnetic field described by the Lagrangian density L=-FαβFαβ/4 After some calculation I find a charge Jαβ that is the angular momentum tensor. So the generator of rotations are (J^{23},J^{31},J^{12}) =...
  26. P

    Electromagnetic wave energy density

    An electromagnetic plane wave has an electric field and a magnetic field. Each component contributes equally to the energy density. Mathematically it is very straight forward to show this is true. The question is, "Fundamentally, why is this true?" Again, I'm not looking for a derivation...
  27. M

    Is an imaginary electromagnetic gauge field something physical?

    Hi, my question is, if there is an interpretation for electromagnetic gauge fields, whose components are imaginary. This would lead to an imaginary magnetic field... Does anything like this exist? Or is it forbidden ny some first principal arguments? Thank you in advance for every input! Melvin
  28. H

    Electromagnetic wave propagation/dissipation

    Hey all, just wondering over a very naive question but I couldn't really find the answer by looking through the web. So electromagnetic waves are self sustaining and they don't lose energy while traveling through space, except if the photons they're made out of do "collide" with matter which...
  29. K

    Electromagnetic induction with two coils and an iron heart

    Homework Statement Two coils are place on an iron heart, like in the picture. The top Coil is connected to a galvanometer, the second could be connected to a power source. Homework Equations Will an electric current flow through the top coil when: a) connecting and then...
  30. Spinnor

    Can the electromagnetic vector potential be written in terms of a complex field?

    Is there a complex field that when properly interpreted yields the four components of electromagnetic vector potential, A_0, A_1, A_2, and A_3? Somewhat along the lines of the complex field ψ yielding information about a particles energy, momentum, and position probability. Thanks for any...
  31. J

    Hey guise, Question about how antennas detect electromagnetic waves?

    Yer.. I'm lazy and tired, did not enough research and found out that the radio/electromagnetic wave makes all the electrons move back and forth when the wave oscillates between the magnetic and electric fields... so you can see how much the current oscillates etc. But... um cameras work...
  32. M

    Electromagnetic Waves: Influence on Electric Wave?

    Can the magnetic wave have an influence on the electric wave?
  33. B

    Time reversal transformation of electromagnetic four-potential

    Consider the time-reversal Lorentz transformation given by the 4x4 matrix: \Lambda_T = \begin{pmatrix} -1 & 0 & 0 & 0\\ 0 &1 & 0 & 0\\ 0 & 0 & 1 & 0 \\ 0 & 0 & 0 &1 \end{pmatrix}. In my relativistic quantum mechanics lecture, we discussed how the electromagnetic 4-potential...
  34. P

    Force of Electromagnetic Radiation and Visible Light

    Is there an equation for force due to electromagnetic radiation? For example, is there a force due to orange light?
  35. D

    How to prove Fardays' law of electromagnetic induction

    Homework Statement Here is a question which frequently occurs on on our school test: "Prove Faraday's law of electromagnetic induction on the basis of principle of conservation of energy" I do not really know how to begin.Thanks!
  36. S

    Describing Electromagnetic Induction of a Guitar Pickup

    First Post! So I was curious about how I could relate my new found knowledge of electromagnetic inductance on guitar pickups and I came across this on the internet: http://www.sciencebuddies.org/science-fair-projects/project_ideas/Music_p004.shtml#background Which says, "All of these...
  37. P

    Energy Density Units Electromagnetic Waves

    Homework Statement In what units is energy density measured? 1. Watts 2. Watts per cubic meter 3. Newtons per meter 4. Joules per cubic meter Homework Equations E = cB (as derived by Maxwell) The Attempt at a Solution This question is so basic yet I'm confused. I thought...
  38. M

    Electric and Magnetic fields at one point on an electromagnetic wave

    At one instant, the electric and magnetic fields at one point of an electromagnetic wave are E = (210 + 320 − 40) V/m and B = B0(7.5 − 7.5 + a) μT. Find a and B0 E=cB The Attempt at a Solution So I found a using E dot product B = 0 and I got the value a=-20.625 and this is...
  39. P

    Electromagnetic Induction (EMI)

    A non conducting ring of mass m and radius R has a charge Q uniformly distributed over its circumference. This ring is placed on a rough horizontal surface such that the plane of the ring is parallel to the surface. A vertical magnetic field B=B0t2 τ is switched on. After 2 second from switching...
  40. A

    Electromagnetic wave in a conductor

    When an electromagnetic wave hits a conductor the transmitted part of the wave is damped considerably. I want to know if anyone can explain physically why the field is attentuated inside the conductor - i.e. what happens. I know the basic properties of a conductor: - Electrons free to roam -...
  41. J

    Amplitude of an electromagnetic wave

    Lets take visible light for example. The frequency/wavelength determines the amount of energy and the type of wave(micro,radio,gamma ect.) The intensity or brightness is determined by the amount of photons. So what does the amplitude determine?
  42. S

    Electromagnetic field in vertical

    Hello, I know the electromagnetic field propagates in a 3D space so if I am horizontally aligned with the field I will receive its variation but what if I'm vertically aligned ? thanks
  43. M

    Needing Tips for Electromagnetic Fields Class

    Just posting to ask if anyone has any tips to give for a student in a Junior level Electromagnetic fields class. We usually get about 10-20 problems/week and I manage to only get 6-7 of them done every time. Also, though I generally do well with it, I'm struggling to find the energy to read...
  44. V

    Why does electromagnetic radiation (energy) excite electrons?

    Hello everyone, I've been told many times that when the right frequency of electromagnetic radiation hits an electron, it is excited to another energy level. My question is this, "why do electrons get excited to higher energy levels when hit by electromagnetic radiation?" Why does the...
  45. C

    Understanding Electromagnetic Waves: From Mechanical Waves to Quantum Mechanics

    I can't represent me mentally what is an electromagnetic wave. I know that a mechanical wave is the propagation of a disturbance in a material medium and mentally I can see what it is. But electromagnetic ... Last year, I did electromagnetism. We studied Maxwell equations and we saw a...
  46. C

    Help With Electromagnet and Air Cores

    hello i need some help, i know very little about EM. i would greatly appreciate any advise u can lend me. i need to make an electromagnet but i am wondering how strong air cores can be? will an air core be able to work on and off continuously for hours at a very high rate of speed, it...
  47. mef51

    The Sun, Electromagnetic Waves, and Gravitational Waves

    This is a question about electromagnetic waves and gravitational waves. Let's say we're on the Earth and we're looking up at the sun (safely). If the sun were --for some reason-- to violently and dramatically jerk from its position, how would we first find out? Would we first *see* the...
  48. R

    How does electromagnetic interference work?

    I have to do a presentation on why cellphones are banned in hospitals, and I'm going to have to explain how electromagnetic interference from the waves a cellphone gives off can mess with medical equipment. Can someone please explain the physics behind this?
  49. A

    What are electromagnetic waves really

    My book takes a look at the maxwell equations in free space, shows that E and B satisfies the wave equation and then guesses on a plane wave as a solution such that you get a tranverse wave with E and B perpendicular to the direction of propagation. I don't know if I am too slow in realizing...
  50. M

    Using Mixed Electromagnetic Boundary Conditions

    Hi As we know, we have two kinds of Electromagnetic Boundary Conditions for interfaces in an electromagnetic problem.one is imposing the continuity of Bz and Hr and the other is applying the continuity of A(Magnetic Vector Potential) and the discontinuity of its derivative with respect to the...
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