Electromagnetism Definition and 853 Threads

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. Hak

    Coaxial semi-infinite solenoid and superconducting disc

    I have no idea how to deal with the problem. Do you have any hints, please?
  2. Hak

    Inductance Puzzle involving coplanar conducting rings

    I solved the first point as ##L_n = \frac{\mu_0 n R}{2}##. How to proceed for the other point?
  3. cemtu

    I How does the electrical field become bent instead of following a straight line?

    Why is electrical field bent like that rather than following a straight line across to the relevant point over there?
  4. cutielollipop

    Electromagnetism question -- Forces between two current carrying wires

    Here is the question. I just wanted to confirm and see if I'm understanding the question clearly. For 3a) I said the first wire would have the magnetic field going in a counter clock wise direction and the second wire would have a magnetic field going in a clockwise direction using the right...
  5. B

    I Power Loss Due to An Eddy Current

    Hi there! Recently, I am studying this kind of power loss from the following link: https://www.electricalvolt.com/2019/08/eddy-current-loss-formula/?expand_article=1 Just to summarize an idea, Supposed that we got a material, which is penetrated by a magnetic flux. The material will generate...
  6. Z

    Understanding example in Wikipedia entry for open circuit voltage

    Consider the circuit (Wikipedia, Open Circuit Voltage) I am having a bit of difficulty understanding the steps and concepts here. I redrew the circuit as follows The red square is the same piece of the circuit with the dotted lines around it in the original diagram (not sure what this is...
  7. Z

    How do we obtain an ampere-hour rating given voltage and watt-hour?

    The solution is thus 0.69 ampere-hours, or 690 mA-hours. Now, as far as I can tell, an ampere-hour is unit of charge. That is we can convert it to coulombs (C). For example, if we have a current of 1A for 1h, then we have 1 C/s x 3600 s = 3600 C = 1 ampere-hour. This is my guess since the book...
  8. Z

    I Understanding dissipation of energy in a resistor through the Drude model

    In section 4.8 entitled "Energy Dissipation in Current Flow" of Purcell and Morin's Electricity and Magnetism, there is the following snippet The model in question is the Drude model I believe (though the book does not seem to give the model any name). There are some paragraphs like this in...
  9. S

    I The vector math of relative motion of wire-loop & bar magnet

    I was watching this video about how the problem of a wire-loop moving relative to a bar magnet: The case of presuming that the wire-loop is fixed seems to be that the magnetic flux (along the surface normal to the direction of the centerline - call it C) through the wire-loop is changing in...
  10. Matthew_

    I Help with Canonical Poisson Brackets & EM Field

    We were introduced the lagrangian for a particle moving in an eletromagnetic field (for context, this was a brief introduction before dealing with Zeeman effect) as $$\mathcal{L}=\dfrac{m}{2}(\dot{x}^2_1+\dot{x}^2_2+\dot{x}^2_3)-q\varphi+\dfrac{q}{c}\vec{A}\cdot\dot{\vec{x}}.$$ A...
  11. D

    B Magnetic field and generator power output

    Hi, I am confused about whether decreasing the magnetic field used for a generator could increase the generator's power output. I used four equations: 1. Torque = Force x radius 2. Torque = NIAB (N = number of turns, I = current, A = area of armature, B = magnetic field). 3. emf =...
  12. R

    B Seeing both B field lines and E field lines at the same time

    After watching this clip Electric Field Lines Lab I wonder if it is possible to see both electric field lines and magnetic field lines at the same time by swapping the two nails in the video with two bar magnets, as the conductors as we understand bar magnets are metals and metals are good...
  13. H

    I Which does more work: gravitation or electromagnetism?

    1: There is a universal gravitational force between two 1 kg iron balls, and the energy generated by their mutual attraction is so small that it is difficult to observe; there is also an attractive force between a 1 kg neodymium magnet and 1 kg of iron, but the energy generated by their...
  14. milkism

    Electromagnetism: Moving conductor and EMF

    For 1) I used $$V=Blv=Blwr$$, where $$w= \frac{4\pi rad}{sec}$$, $$l= 0.30m$$ and $$r=0.50m$$. I got 0.5 V. For 2) I used W=Vq=VIt, where $$q=It$$, where t=0.5 s, we get 1.125 J. For 3) I used P=IV, we get 2.25 W. Are these correct?
  15. F

    I Do you think emissivity of air makes sense?

    Hello guys :)In the frame of finding a physical model for the temperature of Earth's surface, talking about the very "idealized" two-layers model of atmosphere, I ask you now the question to the other physicists or engineers: does it make sens to associate an emissivity to a layer of air (+ some...
  16. Z

    MIT OCW, 8.02 Electromagnetism: Potential for an Electric Dipole

    Here is a depiction of the problem a) The potential at any point P due to a charge q is given by ##\frac{kq}{r}=\frac{kq}{\lvert \vec{r}_s-\vec{r}_P \rvert}##, where ##r## is the distance from the charge to point P, which is the length of the vector difference between ##\vec{r}_s##, the...
  17. milkism

    Magnetic- and Electric- field lines due to a moving magnetic monopole

    Question: My answer: What it looks like for an electric charge: Am I correct? If you want I can hand out my Latex on how I got to it, it will refer to the book Griffiths a lot.
  18. milkism

    Electric and magnetic fields of a moving charge

    Part a) My solution: Big R basically becomes r, and the electric and magnetic field lines are doubled because of superposition principle. Am I right?
  19. G

    Power dissipated by a resistor on a coaxial cable

    I need help with part c. My solution: Is there an other way to do this other than dimensional analysis? P.S "dr an infinitesimal radius", it ofcourse should be dz.
  20. sinus

    I The Method of Images (Electromagnetism)

    Can anyone explain to me why grounded means zero electric potential. I confuse what's the relation between infinite ground conducting plane and its electric potential (the method of images). I have a several question: 1. Why the conductor plane must be infinite, while in reality there's no...
  21. Z

    MIT OCW, 8.02, Electromagnetism: Charged Cylindrical Shell

    Here is figure 2.16.6 Here is the picture I drew to set up the problem My first question is if the reasoning and integrals are correct. I used Maple to compute the three integrals. The first two result in 0, which makes sense by symmetry. Maple can't seem to solve the last integral.
  22. E

    I The implications of symmetry + uniqueness in electromagnetism

    I have tried to follow "Symmetry, Uniqueness, and the Coulomb Law of Force" by Shaw (1965) in both asking and solving this question, but to no avail. Some of the mathematical arguments there are a bit too quick for me but, it suffices to say, the paper tries to make the "by symmetry" arguments...
  23. L

    Two charged spheres hitting each other

    Since the forces involved (gravity and electric force) are conservative we can use conservation of energy. The initial energy is ##E_i= k\frac{q_1q_2}{r_0}-G\frac{m^2}{r_0} ## and the final ##E_f=mv^2+k\frac{q_1q_2}{2r}-G\frac{m^2}{2r} ## so from ##E_i=E_f ## we get...
  24. T

    Hall effect over a conducting ring

    This is the diagram provided in the question: The ring is made of conducting material. I was originally asked to find the potential difference between ##a## and ##b##. I did so using the Hall effect (and assuming it would work as per normal in this situation). This got me ##\Delta V = vBl##...
  25. P

    Radiation emitted by a decelerated particle

    Honestly, folks, I don't even know how to start. I included in the Relevant Equations section the relativistic generalization of the Larmor formula according to Jackson, because that's the equation for the power emitted by an accelerated particle, but I don't see how that gets me very far. The...
  26. S

    I Can trains use permanent magnets to be propelled?

    Can a train (e.g. like a maglev train) use a set of permanent magnets (not electromagnets) that somehow can be propelled and maintain at least a constant speed with them? Is this an example of such system...
  27. sol47739

    I Exploring Electromagnetism & Quantum Mechanics

    In classical electromagnetism I think I have understood the following(please correct me if something is wrong): A charge produces an electric field, a charge moving with constant velocity produces a magnetic field, an accelerating charge emits electromagnetic radiation. In radio antennas this is...
  28. warhammer

    I Query on Electromagnetic Theory (Dielectric Boundary Conditions)

    The given question from Electromagnetic Theory (which is based on Dielectric Boundary Conditions) is as follows: Interface b/w two dielectric medium has a surface charge density (suppose xyz C / (m ^ 2) ). Using boundary condition find field in 1 (relative permittivity =xyz) if field in 2...
  29. bigmike94

    Advancing to Higher Level Electromagnetism: Is Purcell & Morin the Solution?

    Hi I am coming up to the end of first year electromagnetism using the book University Physics. I will be honest there’s a lot of information crammed into a few hundred pages and it was my first ever exposure to EM. I never did it in school. I feel like its give me a good overview but i don't...
  30. L

    Conducting rod in equilibrium due to magnetic force

    I am having problems understanding point (b) so I would like to know if my reasoning in that part is correct and/or how to think about that part because I don't see how to justify the assumption ##v_y=0\ m/s##. Thanks. I set up the ##xyz## coordinates system in the usual way with ##xy## in the...
  31. L

    Current through ring in solenoid-ring system

    The following is my solution to this problem; I would appreciate some feedback, especially on part (b), which I have found the most challenging. Thanks. (a) Using Ampere's Law I get ##B=\mu_0 n i_1## where ##i_1## is the current through the solenoid, and since ##\phi=Li_1##, where ##L## is the...
  32. X

    I Magnetic field strength of a stack of magnets

    I know that for a single cylindrical neodymium magnet, the formula $$ \displaystyle{\displaylines{B(z)=\frac{μ_0M}{2}(\frac{z}{\sqrt{z^{2}+R^{2}}}-\frac{z-L}{\sqrt{(z-L)^{2}-R^{2}}})}} $$ shows the relationship between the magnetic field strength and the distance between the magnet. I was...
  33. warhammer

    I Electric Field & Interplay between Coordinate Systems | DJ Griffiths

    Hi. I believe I have what may be both a silly and or a weird query. In many Griffiths Problems based on Electric Field I have seen that a coordinate system other than Cartesian is being used; then using Cartesian the symmetry of the problem is worked out to deduce that the field is in (say) z...
  34. Salmone

    I How an induced electric dipole vibrates with EM field

    If we have an electromagnetic wave like the one in the picture and a molecule which is, in the image, the small black ball with electron cloud being the part with "minus sign" in it, does the molecule with its cloud start to oscillate, once the EM wave hits it, as an induced electric dipole...
  35. L

    Maximum charge on the plates of a capacitor

    What I have done: The electromotive force due to Faraday's Law is: ##\mathcal{E}=-\frac{d\phi(\vec{B})}{dt}=\frac{d}{dt}(Ba^2)=a^2\frac{dB}{dt}=-10^{-4}V.## In the circuit, going around the loop in a clockwise fashion: ##\oint_{\Gamma}\vec{E}\cdot d\vec{l}=-\frac{d\phi(\vec{B})}{dt}\Rightarrow...
  36. V

    Trying to understand electromagnetism

    Hi! I'm trying to understand electromagnetism. Please help me. Say we have an electron start moving a sine wave like pattern along z axis with amplitude of 1m up and down with frequency equal to 100Mhz. I want to determine an electric and magnetic field vectors in any arbitrary point in any...
  37. Adgorn

    Relativistic particle in uniform magnetic field (solution check)

    My solution was as follows: $$\frac {d\overrightarrow p} {dt}=q \frac {\overrightarrow v} {c}\times \overrightarrow B_0$$ The movement is in the ##[yz]## plane so ##|\overrightarrow v\times \overrightarrow B_0|=vB_0##, therefore: $$\biggr |\frac {dp} {dt}\biggr |= \frac {qvB_0} {c}.$$ On the...
  38. L

    Force to apply to a loop moving away from a current-carrying wire

    What I have done: (1) ##\Phi(\vec{B})=\int_{S}\vec{B}\cdot d\vec{S}=-\frac{N\mu_0 il}{2\pi}\int_{s=h}^{s=h+l}\frac{ds}{s}=-\frac{\mu_0iNl}{2\pi}\ln(\frac{h+l}{h})## so ##\mathcal{E}=-\frac{d\phi(\vec{B})}{dt}=-\frac{\mu_0iNl^2v}{2\pi h(h+l)}## so...
  39. L

    Solving Equation to Analyze Steady State Current

    I set up the equation ##V-iR-L\frac{di}{dt}=0##, with ##i(0)## and by solving it I got ##i(t)=\frac{V}{R}(1-e^{-\frac{R}{L}t})##. Then, since the steady state current is ##i_s=\frac{V}{R}## I imposed the condition ##i(t_1)=\frac{9}{10}\frac{V}{R}\Leftrightarrow...
  40. L

    Help Needed for Solving Electrical Circuit Problem

    What I have done: (1) ##I(0)=\frac{V}{R}=\frac{1.5}{25}A=0.06 A.## (2) By setting ##I(t*)=0.06(1-e^{-(35/0.4)t*})=35 mA## we get ##t*\approx 0.01 s## What I have done seems correct to me, but the result for part (2) should be different. I would be grateful if someone could point out to me...
  41. L

    Flux of constant magnetic field through lateral surface of cylinder

    If the question had been asking about the flux through the whole surface of the cylinder I would have said that the flux is 0, but since it is asking only about the lateral surfaces I am wondering how one could calculate such a flux not knowing how the cylinder is oriented in space. One could...
  42. L

    Calculating Electric Potential and Energy in a System of Spherical Conductors

    (a) Using Gauss's Law ##E_P=\frac{q_1+q_2+q_3}{4\pi\varepsilon_0(R_1+R_2+R_3+d)^2};(b) V_3-V_1=\int_{R_3}^{R_2}\frac{q_1+q_2}{4\pi\varepsilon_0 r^2}dr+\int_{R_2}^{R_1}\frac{q_1}{4\pi\varepsilon_0 r^2}dr=\frac{q_2}{4\pi\varepsilon_0}\left(\frac{1}{R_3}-\frac{1}{R_2}\right).## (c)...
  43. L

    Conducting cable surrounded by two cylindrical shells

    What I have done: (a) If we start at ##R_5## then we have ##\Delta V=-\int_{R_5}^{R_1}\vec{E}\cdot d\vec{l}=-(\int_{R_5}^{R_4}\vec{0}\cdot d\vec{l}+\int_{R_4}^{R_3}\frac{\lambda}{\varepsilon_0}dl+\int_{R_3}^{R_2}\vec{0}\cdot d\vec{l}+\int_{R_2}^{R_1}\frac{\lambda}{\varepsilon_0}dl=-\lambda(...
  44. SBrownJC

    B Do materials surrounding magnets affect how superconductors levitate?

    I'm currently doing an experiment with magnetic levitation but I don't know if my independent variable will even affect my results at all. I am planning on building a rail of magnets and levitating a type 2 superconductor on it. I wanted to change the material surrounding the rail of magnets...
  45. Zaitul Hidayat

    How Do You Apply Zonal Spherical Harmonics in Electromagnetism Problems?

    I don't really understand how to find the solution. I've tried to find the solution in books and google but still can't find it. In general, the Question 1 the problem is using the method of Image charge and Induced surface charge density. but this time my professor changed it to something else...
  46. J

    Lagrangian with a charged, massive vector boson coupled to electromagnetism

    I need to use hermiticity and electromagnetic gauge invariance to determine the constraints on the constants. Through hermiticity, i found that the coefficients need to be real. However, I am not sure how gauge invariance would come into the picture to give further contraints. I think the...
  47. DC2

    A Calculation of EM fields induced by an antenna in the near field

    The title pretty much covers it. I'm having to calculate the field induced inside the human body by an antenna in the near field (essentially, a phone placed close to a user's head), and I'm drawing a blank on how to relate the field generated by the antenna to the field induced inside the...
  48. Jd1431

    I What makes a plasma collisionless?

    Hi, I'm trying to understand what determines whether a plasma will be collisionless or collisional. I understand that a diffuse plasma with large mean free path will be collisionless but I don't really understand it from an electromagnetic point of view
  49. G

    Flux of the electric field that crosses the faces of a cube

    a) $$\phi_T=\phi_F-\phi_I=10^4\cdot 4\cdot 4-10^4\cdot 4\cdot 4=0\, \textrm{Nm}^2/\textrm{C}$$ b) $$\phi_F=\underbrace{300\cdot 4}_{\vec{E}}\cdot \underbrace{4\cdot 4}_{\textrm{area}}=19200\, \textrm{Nm}^2/\textrm{C}$$ $$\phi_0 = 300\cdot 0\cdot 4\cdot 4=0\, \textrm{Nm}^2/\textrm{C}$$ Then...
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