Electromagnatism Definition and 56 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. W

    I Magnetization inside a diamagnetic material antiparallel to ##B_{ext}##

    Let's say I have a constant magnetic field and I dive into it a diamagnetic material. Griffiths says that in the presence of a magnetic field, matter becomes magnetized and it will be found to contain many tiny dipoles with a net alignment along some direction. However, what's exactly the link...
  2. 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##...
  3. physicks885

    Minimum seperation of two electrons moving toward each other

    [Mentor Note -- Two threads started by partners in a class have been merged into this one thread, since they are working on a shared solution to turn in]
  4. 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...
  5. S

    Convection current in electricity

    So, I randomly came upon this in a textbook that I was skimming and I think I have a very very surface ideea of what it's about but I want to read and know more in order to understand the fenomenon in much more detail. Any help in any form would be much appreciated! P.S.: This is my first post...
  6. E

    Magnetic energy inside a coaxial cable

    Hi, I have to find the magnetic energy inside a coaxial cable of inner radius ##a## and outer radium ##b##, ##I = I## By using Ampere's law if ##r<a## ##B = \frac{\mu_0Ir}{2\pi a^2}## if ##a<r<b## ##B = \frac{\mu_0I}{2\pi r}## if ##r>b## ##B = 0## Then, the energy in a magnetic field ##E_b...
  7. T

    Tensor help -- Write out this tensor in a simplified sum

    I managed to write $$F_{\alpha\beta}F^{\alpha\gamma}=F_{0\beta}F^{0\gamma}+F_{i\beta}F^{i\gamma}$$ where $$i=1,2,3$$ and $$\gamma=0,1,2,3=\beta$$. How do I proceed?
  8. W

    How far do gamma rays extend from an accelerator?

    According to https://www.osti.gov/servlets/purl/7234564, the HERMES III which stand for High Energy Radiation Megavolt Electron Source accelerator is "capable of delivering a peak dose of ~100 krad (CaF2) over a useful area of ~1000cm2 (area where dose is greater than 50% of the peak dose) in a...
  9. S

    Force acting on a current carrying conductor within a magnetic field

    I am new to this forum, and this is my first post. Please bear with me if my query has any inaccuracies. In the attached figure, a coil is wrapped around the central arm of a flat H-shaped thin metallic plate (such as iron). DC current flows through the coil and magnetizes the arm. At the...
  10. J

    Conservation of energy in transformers

    This question is given as an exercise in my book. I can't figure out whether this is a poorly worded question or if I misunderstand. The answer I can come up with is that power is dissipated over the load so more power is needed to be supplied by the ac source. This seems too hand-wavy to me...
  11. dom489

    How can I increase the wavelength of light photons?

    Summary:: need to increase the wavelength of light. I am an intro physics student working on a project and need to increase the wavelength of photons. I only have visible light sources available but need to have an emission of a wavelength larger than 1mm. is there a way to shift wavelength...
  12. astroman707

    Studying What's the best way to apply the concepts learned in physics 2?

    I'm finishing up physics 2(intro E&M) at my college, and I'd like to apply the concepts I learned in it over the summer. I was considering working through an electronics book, or building a radio, etc. What kind of projects or books do you recommend to cement some of the topics I learned in a...
  13. P

    Is there any evolutionary benefit from magnetoreception?

    Some organisms still have magnetoreceptors, what would be the evolutionary benefits of these receptors?
  14. JD_PM

    Average electric field over a spherical surface

    Homework Statement I was working out problem 4, chapter 3 of Introduction to Electrodynamics by Griffiths: a) Show that the average electric field over a spherical surface, due to charges outside the sphere, is the same as the field at the centre. b) What is the average due to charges inside...
  15. A

    What is the magnetic field generated by these two particle beams?

    A uniform beam of positively charged particles is moving with a constant velocity parallel to another beam of negatively charged particles moving with the same velocity but in opposite direction separated by a distance d. Then, how should be the variation of magnetic field B along a...
  16. Silverhobbiest

    I Significant Physical/Chemical Change Found by Sign Reversal?

    We know that "plastic" and "glass" charges were arbitrarily assigned to be negative and positive respectively, and electrons and protons were given their charges based upon that assignment (According to Randall D. Knight in Physics for Scientists and Engineers). I am curious if any significant...
  17. thariya

    A Quantization of the electric field inside a box

    Hello all, The second quantization of a general electromagnetic field assumes the energy density integration to be performed inside a box in 3D space. Someone mentioned to me recently that the physical significance of the actual volume used is that it should be chosen based on the detector used...
  18. T

    Deflection of wave in dissipative media with a complex refractive index

    Homework Statement A monochromatic plane wave with wavelength 500µm is propagating through a dissipative medium with refractive index 1-0.0002i. It approaching the edge of the medium, and will pass out into free space. If the angle of incidence is not 90°, how much will the wave deflect as it...
  19. astroman707

    I What math topics should one master for first year physics?

    I’ll be taking the year long physics sequence at my college this fall and I want to know what specific math topics I should master, so that I can conquer my first year of physics. I’m planning to brush-up on any necessary topics from algebra, through precalc, and including calc 1. It’s an honors...
  20. A

    Poynting vector - uniform vs accelerated charge

    I am trying to understand why an accelerating charge emits radiation/electromagnetic waves but a uniformly moving one does not. I saw one video on Youtube where it seemed that it was explained by the fact that with a uniformly moving charge the Poynting vector was pointing 'in to the volume' -...
  21. A

    I Do hot objects always glow?

    I'm talking hotter than T = 6000k. The higher the temperature, the more the curve in the attached figure would shift to the left (while at the same time getting higher). So the intensity peak would eventually fall back into the invisible portion (very small wavelength this time) of the...
  22. S

    Jump conditions for electric field across an interface

    Hi, I have some confusion about the jump conditions for an electric field across an interface between two materials with different properties. In general, we have the two jump conditions across an interface: n.(ɛE)+ - n.(ɛE)- = σ...
  23. H

    Plasma ball electric shock mystery

    Plasma ball has a high voltage. Why don't we get an electric shock when we touch it?
  24. S

    How to calculate total cross section from differential cross section

    I was doing the calculations for this: http://fermi.la.asu.edu/PHY531/cylinder/index.html But I can't figure out how to go from \frac{d\sigma}{d\phi} to the total cross section. My guess was that you did the integral from \phi=0 to \phi=2\pi, but that's not helping since I can't tell either how...
  25. Toby_phys

    Energy of a solenoid with a partially removed core

    Homework Statement A solenoid of volume V, current I and n turns per unit length has an LIH core, relative permitivity is \mu_r. This core is then slid out so that a fraction f of the solenoid's length is filled with air/vacuum (and 1-f is filled with the core). Neglecting hysteresis, what...
  26. F

    Please clear my electromagnetism doubt about units

    It is a well known fact that, in electromagnetic units, strength of a shell and strength of current flowing through its boundary are same. See here. \begin{equation} \begin{matrix} \text{i.e.}\: i \text{(biot)} = \phi \text{(biot) } \end{matrix} \tag{1} \end{equation} (a) While converting to...
  27. Zohaib_aarfi

    I Correct relation is F^{ij} = - epsilon^{ijk} B^k.

    When I tried to derive this relation I got the wrong sign. Please check the pic and tell me my mistakes.
  28. L

    How do I apply Maxwell's equations?

    For example, if I have a magnetic field perpendicular to some surface and I change this magnetic field with constant speed, how do I calculate the Electric field at any point on this surface, since ∫E⋅ds=k, where k is some constant, could be done with many different vector fields.
  29. Angelo Cirino

    I Laplacian in integration by parts in Jackson

    I am reviewing Jackson's "Classical Electromagnetism" and it seems that I need to review vector calculus too. In section 1.11 the equation ##W=-\frac{\epsilon_0}{2}\int \Phi\mathbf \nabla^2\Phi d^3x## through an integration by parts leads to equation 1.54 ##W=\frac{\epsilon_0}{2}\int |\mathbf...
  30. A

    Finding E and B field of a weird charge distribution

    Homework Statement Initially there is a spherical charge distribution of with a radius ##R_0## and uniform charge density ##ρ_0##. Suppose the distribution expands spherically symmetrically such that its radius at time t is ##R_0 + V t##, where V is the velocity. Assuming the density remain...
  31. V

    Boundary condition for electrostatics problem - found issue?

    Hey everyone Just a picture of my configuration. The assumption here is $$\epsilon_a,\epsilon_b,\epsilon_c$$ are different from one another. Really the interest of this problem is to find the scalar potential $$\phi$$, such that $$\nabla^2 \phi = 0$$. So now my question, about jump...
  32. AaromTheBritt

    I Lenz's Law

    I'm working on induction at the moment, and the math makes sense, but Lenz's Law is giving me trouble. Does anyone have an easier way (relatively) of remembering the directions of emf? Any advice is appreciated.
  33. D

    How photons exceeds their velocity?

    Is there a theory that explains the mechanism under which photons exceeds the speed of light? It should refer to cases including photons generated in an oscillating charges, dipoles, inhalations, different kind of excitation, accelerated particles, scattering phenomenons etc. Please note that...
  34. O

    Electrons moving in an electric field

    Homework Statement Suppose electrons enter the electric field midway between two plates at an angle θ0 to the horizontal, as shown in the figure, where L = 5.1 cm and H = 1.1 cm. The path is symmetrical, so they leave at the same angle θ0 and just barely miss the top plate. What is θ0? Ignore...
  35. physicality

    I How to show that Electrodynamics is conformally invariant?

    [Moderator's note: changed thread title to be more descriptive of the actual question.] Consider Maxwell's action ##S=\int L## over Minkovski space, where the Lagrangian density is ##L = -\frac{1}{4}F_{\mu\nu}F^{\mu\nu}##, and the Electromagnetic tensor is given by ##F^{\mu\nu} = \partial^\mu...
  36. S

    What is the value of induced magnetic field?

    Homework Statement Two coencenteric metalic shell has inner radius $r_1$ outer radius $r_2$. We place along axis infinity wire has $\lambda$ charge in per unit length. The inner region of metalic shells inserted with relative permabilitty coefficent $\epsilon$. This system rotates with $\omega$...
  37. fabiogn

    Current and magnetic field in a spherical capacitor

    << Mentor Note -- Thread moved from the technical forums,. so no HH Template is shown >> Hello! I have a question on Electromagnetics. Could anyone check if I am on the right track? Here is the proposed problem: Consider a spherically symmetric current distribution, which is radial and...
  38. AmishaPanchal

    How to convert movemnt/speed to electricity or other E.forms

    Hi I was wondering if there is a way to produce energy using the movement of vehicles on the road. I do not know which principles can come into picture, but I believe Electromagnetism/ detection is the way to go? If someone could at least throw me in the right direction of which field to...
  39. Titan97

    Energy and momentum imparted by an EM wave

    Homework Statement A plane electromagnetic wave is incident on a material surface. The wave delivers a momentum ##p## and energy ##E##. Then which of the following is/are correct? 1) ##p=0,~E=0## 2) ##p\neq 0,~E=0## 3) ##p=0,~E\neq 0## 4) ##p\neq 0,~E\neq 0## Homework Equations None The...
  40. DrPapper

    Potential of a Rectangular Pipe by Laplace's Equation

    Homework Statement Homework Equations Is my part a correct and am I on the right track for part b? If not please give me some suggestions to get me closer to the right track. Also, how would I even begin c.? We have literally done no examples like this in class. The Attempt at a Solution...
  41. recursive

    Capacitor Energy With Different Dielectrics

    Homework Statement Two parallel plates are connected to a battery which maintains a constant potential difference of 12.0 V. The distance between the plates can be varied and there are three plates of different dielectric materials available: rubber (0.40 mm, κ = 6.7), glass (4 mm, κ = 7) and...
  42. Brennen berkley

    Electric field between inner and outer cylinder

    Homework Statement A capacitor is constructed of two long concentric metal cylinders, each having length of 1.0 meters. The inner cylinder has a radius R1 = 1.0 cm, and the outer cylinder has a radius R2 = 1.25 cm. The hollow space between the two cylinders is filled with nylon having a...
  43. Brennen berkley

    Proof that disk of charge = point charge when very far?

    Homework Statement Take the expression 21.11 (pictured below, specifically the bottom one) for the electric field above the center of a uniformly charged disk with radius R and surface charge density σ, and show that when one is very far from the disk, the field decreases with the same square...
  44. J

    Refraction index

    Homework Statement Within a certain material, an EM wave with = 1 mm is attenuated to 10% of its original intensity after propagating 10 cm. Determine the imaginary part of the index of refraction ni Homework Equations 3. The Attempt at a Solution [/B] so...
  45. 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...
  46. E

    Modes orthogonality in a dielectric slab

    A typical mode in a dielectric slab like this, with propagation along x, uniformity along z and refractive index variation along y, is represented by the following function: f (y) = \begin{cases} \displaystyle \frac{\cos (k_1 y)}{\cos (k_1 d)} && |y| \leq d \\ e^{-j k_2 (y - d)} && |y| \geq d...
  47. S

    Magnetic field of a long solenoid

    Homework Statement A long solenoid has current I flowing through it, also denote N as the turns per unit length. Take its axis to be the z-axis, by symmetry the only component of the magnetic field inside is Bz. Find the magnetic field at the center of the solenoid (on the axis). Also, find the...
  48. S

    Potential inside a sphere with two regions

    Homework Statement Suppose a charge is distributed in a lower half region of a sphere and the upper half has zero charge. What is the potential inside? Homework Equations Poisson Equation? The Attempt at a Solution My problem here is I don't know how to start, I think laplace equation can't...
  49. E

    Wave reflection and refraction, relations between angles

    Hello! This post is strictly related to my previous one. Let's consider the same context and the same image. Regarding the oblique incidence of a wave upon an interface between two dielectric, all the texts and all the lectures write an equation like the following: e^{-j k_1 y \sin \theta_i} +...
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