# What is Electromagnetics: Definition and 150 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. ### I When do classical mechanics and electromagnetics stop working?

I've heard that classical mechanics and electromagnetics are not applicable at small sizes in particle physics. 1) At what size and energy levels are they no longer considered to be applicable at all? 2) What range of size and energy levels could be considered a "transition" area where both...
2. G

### Surface current on a spherical superconductor

I need help with part b. My solution: Have I done it right?
3. ### Prerequisites for Fundamentals of Applied Electromagnetics by Fawwaz T. Ulaby

I would like to tackle E&M from a more applied perspective, my maths background is calculus 1, 2 & 3, basic differential equations, basic linear algebra etc. physics background i have completed intro physics that involved very basic circuits etc but nothing major in the sense of applied...
4. ### I Question about electromagnetics (waves and particles)

I saw that we can talk about the light as particles (photons ) or as an electromagnetic wave , the question is that do we represent other electromagnetic waves (like microwaves or radio waves ) as particles (like we do with light ) ?
5. ### I Help with electromagnetics: the Poynting Vector and Ampere contradiction

According to equation (2.33) divergence of the Poynting vector or the outflow of electromagnetic power is equal to the stored magnetic field, stored electric field and ohmic losses. My contradiction is the following: Inside a steady state DC current carrying wire, there will presumably be a...
6. ### Electromagnetics: find D,E,P between two parallel conducting plates

I tried to solve this problem on my own, but I'm not sure whether I solved correctly or not. it is electromagnetics homework from my Uni, and it is pretty tough for me. I attached the image of the problem and how I tried to solve this one. I hope somebody will give some feedback.
7. ### Engineering Need help about the magnetic field near an infinite current sheet

here is the question, don't mind about point (a) and (b) because i have solved them already...the main problem is the question on point (c) : so far, what i have done is : H = 2.7*0.1-(1.4*0.15+1.3*0.25) = -0.265 az A/m which is the wrong answer compared to the solution provided from the...
8. ### Classical Best undergraduate electromagnetics textbook

Hi I am looking for a textbook that covers most of the topics in a general undergraduate electromagnetics course. It would be great if the topics below are covered. I don't mind getting a few but would like to find a good explanation of these topics. thanks Gauge invariance Lorenz gauge Greens...
9. ### Fresh air (vacuum) as media for electromagnetics, can it have losses?

Recently I saw an exercise on electromagnetics (plane waves) in which it was said that a plane wave was traveling through vacuum (ε0 and μ0) BUT with losses, i.e, σ ≠0. Is that possible? I think I have read in the past that it's OK in some texbook, but now, I have searched for it in a couple of...
10. ### At least One Faraday Tube Between Every Two Unlike Charges in the Universe

By Classic Coulomb's Law there exists negligible yet non zero force of attraction between two unlike charges in-spite of the distance. However for electrostatic attraction to work we need at-least one Faraday Tube(Lines of Forces) between the attracting charges, does that means...
11. ### A Maximum reception/transmission criteria for Conical Horn Antennas

I have written a solver for my thesis which determines various parameters of a conical horn antenna for astronomy application. It is done with Mode Matching Technique (MMT) and some Rumsey's integrals for the aperture free space transitions. I have made some goal functions with the solver which...
12. ### A Spectral domain double integral with singularities

The integral looks like Y_{mut, mn} = -j^{m+n}nm \int_{-\infty}^{\infty}\int_{-\infty}^{\infty} \frac{2 ab (k^2 - k_x^2) \sin^2(\frac{k_yb}{2}) \cos^2(\frac{k_xa}{2})}{\omega \mu k_z (\frac{k_yb}{2})^2 [(n\pi)^2 - (k_xa)^2][(m\pi)^2 - (k_xa)^2]} dk_x dk_y Here, k_z = -1j \sqrt{(-(k_0^2 -...
13. ### Exploring the Interaction of Magnetic and Electric Fields

Hello, If you have an appropriately oriented conductive ring in a constantly changing magnetic field, current will flow in the ring. There will also be a magnetic field associated with the current in the ring. I understand (maybe ... ) that the current is due to the electric field which is...
14. ### I Intuition behind fields in Transmission lines

How can traveling wave exist on transmission line if wires are perfect conductors (how voltages can be different at different positions on one perfect conductor)? I mean electric fiels should be zero on equipotential source. I know if length is too long compared to wavelength, we get phase...
15. ### A Waveguide Junction TM/TE combination

In the paper here, it says no matter what the waveguide structure is, if the smaller waveguide has a TM mode and the larger has a TE mode, then the coupling (Inner cross product \int\int_{S_{smaller-waveguide}} (E^{small}_{transverse} \times H^{large}_{transverse}) . \hat z dS, where z is the...
16. ### A Integration of Bessel's functions

I can only find a solution to \int_{0}^{r} \rho J_m(a\rho) J_n(b\rho) d\rho with the Lommel's integral . The closed form solution to \int_{0}^{r}\frac{1}{\rho} J_m(a\rho) J_n(b\rho) d\rho I am not able to find anywhere. Is there any way in which I can approach this problem from scratch...
17. ### Electromagnetics question - magnetic field and electrolysis

Hi everyone, I am most likely the least scientifically minded person to ever have visited these forums! I'm here with a question that I hope someone more scientifically minded can answer for me. If a pair of plastic coated axial neodymium magnets are installed either side of a sheet of alloy...
18. ### How to find the Braking Torque of an Eddy Current Braking Setup?

Homework Statement: Finding the braking torque applied on a moving disk as a result of the Eddy Currents Homework Equations: $$F = \sigma v V B^2$$ So right, Basically my problem is how to find the torque exerted by an eddy current braking setup. My setup consists of a disk rotating on an...
19. ### How to measure electric and magnetic fields in asymmetric capacitors?

Summary: I need to build an asymmetric capacitor, but the mathematics of electromagnetics become too tough, do you have any info that can help? Appreciate it! Hello, I am an undergraduate student in engineering and I want to build an asymmetric capacitor, so I need electromagnetics which I...
20. ### Need a help at computational electromagnetics

Hi dears I study numerical electromagnetics , especially FDTD method , i reached to the point at where i introduce my sources then i get an understanding problem .. at this method ( as in the attached photo ) the electric field is defined at time (t) and magnetic field at (t+dt/2) and there is...
21. ### Changing Acceleration in an Electromagnetics question

Homework Statement Hello. I'm stuck on some question, will glad if you can give me a little hint. The problem is this: A charge -q is located at the distance 's' above a plane, which charged in a positive charge density for area unit σ > 0 . There is a sphere with the radius R charged on a...
22. ### E-field generated by constant current in a circular loop

Homework Statement Discussions of the possibility of a tangential E-field external to a current-carrying conductor must include a voltage source and a return path. Here the problem is reduced to (we believe) the simplest possible geometry. Assume that a circular conducting loop has constant...
23. ### Solving 2D FEM Error with Maxwell Version 17

Hi, I am working on Maxwell version 17. I have a simple motor to analysis 2D FEM. However, when I analyze the model, I see this error. "Maxwell2d solver, process solver2d error: Internal Solver Error: 'Transient solver handles only isotropic conductivity!'. (7:07:10 PM Apr 16, 2018)" I am...
24. ### Electromagnetics wireless transmission of Energy

There is an LC resonant tank connected at a power source at the resonant frequency and far away from it there is Another LC circuit with the same resonant frequency connected to a multimeter. Assuming that there is no resistance and that all components are ideal the second coil will receive all...
25. ### Best Textbook on Electromagnetics

G'day, I am here to seek advice on a textbook for my second-year undergraduate course in electromagnatic field theory. My concern with the recommended textbook is that it isn't easy to read. Any author that proceeds through a proof by simply stating "Next, taking the curl of..." doesn't offer...
26. B

### Induction via Infinite sheet of Current

My thoughts are concerning an infinite sheet carrying current in a direction. I wish to induce a unidirectional electric field outside of the sheet via induction. My ideas were that if the current was changed linearly in a sawtooth fashion, then I would achieve the induced electric field in...
27. ### Textbooks for Electromagnetics, Dielectrics, Magnetic field and Polarisation

I am a Graduate student in Electrical Engineering. I have to work on Electromagnetic, Dielectric, Magnetic field and Polarization for my project. But my problem is I do not have a good background in this course. Now, I really need it in graduate level. My question is, can you guys introduce me a...
28. ### How do changing magnetic fields affect the speed of motors?

Motors are supposed to rotate inside because of changing magnetic field.. but when looking at high speed fan.. I'm thinking how can the changing magnetic field responds so quickly... is the rotation or changing magnetic/electric field the same speed as the fan?
29. ### [Electromagnetics] E-Fields & Equipotential Surfaces

Homework Statement This is from the book Engineering Electromagnetics by Hayt & Buck.[/B] Homework Equations E = - (ΔV/ΔL)[/B]The Attempt at a Solution At part (a), I took the potential difference between point A and the point directly above at the higher surface (106 V) and plugged in the...
30. ### Voltage across switch in LR circuit as switch is opened?

1. I thought that when switch was closed, voltage at the right side of switch was 0 and long time after the switch is open, the voltage at the right side of the switch becomes 0. 2. After the switch is open ecause of the inductor, voltage at the right side of the switch is εL = induced emf So...
31. ### How to calculate the Electric Field due to Capacitors?

I have a problem that I have encountered during research. The setup for this scenario is that I am placing two contacts on top of a piece of diamond. What I need to be able to do is calculate the Electric Field at a point within the diamond when I apply a voltage to the contact. The point of...
32. ### EI Core electromagnet questions

Hello. I am trying to design an EI-core electromagnet (think two c-shaped cores with their gaps abutting). The coils would go on the top and bottom legs of the E (legs B and C in my sketch). There is a sketchbelow and you can find one here...
33. ### Help with basical electromagnetics

Hey guys, can someone please help me with this? In the case of the line charge (pictures 1 and 2), can someone please explain to me how he converted the vector R from cartesian coordinates to cylindrical coordinates without doing any calculation? Also, on the case of the sphere (pictures 3 and...
34. ### [electromagnetics] Lorentz Gauge

I am trying to derive the potential based Lorentz gauge, but I am not sure if I am on the right track. Why the second partial derivative of vector potential must be 0? Please correct me where I got this wrong.
35. ### Electromagnetics: Plane Wave Propagation, Unknown Medium

Homework Statement Based on wave attenuation and reflection measurements conducted at 1MHz, it was determined that the intrinsic impedance of a certain medium is , and the skin depth is 2m. Determine: a) The conductivity of the medium b) The wavelength in the medium c) The phase velocity...
36. ### Master's in Electromagnetics for Biomedical Devices?

My ultimate goal is to come out with the knowledge of being able to create electronic non-invasive medical devices. I'm more interested, in say, detecting chemical compounds in the blood. From the course listing, it seems that Electromagnetics will prepare me for creating antennas, wireless...
37. ### (Simple Electromagnetics) A charge placed between 2 charges

Homework Statement A charge (q) is placed in-between two other equal charges named Q. Q-----q-----Q a) If both Q's are positive, is charge q in equilibrium? If yes, is it a stable or unstable equilibrium? b) What about if one Q is negative while the other is...
38. ### Electromagnetics: Non-Symetrical coil with external iron

Hello, and thanks for looking at my question. For starters, this is NOT a homework question, or a question I will receive any credit for except maybe a "hey, cool". The level of difficulty is roughly a junior-year Electromagnetics class homework quesiton, I suppose? My Question is rather...
39. ### [Electromagnetics] Dielectric boundary condition

http://local.eleceng.uct.ac.za/courses/EEE3055F/lecture_notes/2011_old/eee3055f_Ch4_2up.pdf [Broken] (Page 4.4 )I am having a trouble with understanding why closed loop line integration is 0 at dielectric boundary. As far as I know, closed loop line integration is 0 because electric field is...
40. ### When can I use Helmholtz equation for electromagnetics

The complete Maxwell wave equation for electromagnetic field using the double curl operator "∇×∇×". Only when the transverse condition is hold, this operator can equal to the Laplace operator and form the helmholtz. My question is what's the condition can we use the helmoltz equation instead of...
41. ### [Electromagnetics] Divergence of Current density

eq.1 eq2. eq.3 eq.4Hello, I have a question about eq.4 If we find the closed surface flux integral of J, would it be current?
42. ### Signals and Systems + Electromagnetics classes

Hi All, I am a EE student and thinking about doing the following classes in Spring 16 - Signals & Systems + Electromagnetic + Physics 3. Any suggestions is Emag and Signal and systems very hard?, what Math do you need? (Dif Eq) Is it a bad a idea taking these classes at the same time...
43. ### How to correctly identify r and r' in electromagnetics

Homework Statement This is more of a general problem that I noticed I constantly fail to get right, and seems like something quite basic in vector calculus but it mostly affects me in my electromagnetism class. Whenever I try to work on a problem that involves figures and objects in space, I am...
44. ### Electromagnetics: Moving loop in a static magnetic field

Homework Statement A conducting square loop (L × L) moving with velocity vo ay m/s where the magnetic flux density is B=Bo ax Wb/m2 in 0 < y < 2L, and is equal to zero when 0 > y and y > L. Determine the current in the loop and plot its magnitude as a function in the loop's position in the...
45. ### Current flowing through a loop due to an infinite wire

Homework Statement An infinitely long wire carrying a 1 A current in the positive x direction is placed along the x-axis in the vicinity of a 5-turn circular loop located in the x-y plane as shown in the figure. If the magnetic field at the center of the loop is 0, what is the direction and...
46. ### Classical Cheng's or Lorrain/Corson's Electromagnetics book?

Hello, I want a book on electromagnetics for my second course on electromagnetism. In my first course we used Griffith's "Introduction to Electrodynamics" with supplements like Morin and Purcell's "Electricity and Magnetism". I borrowed those from the university's library but now I want to step...
47. ### Learning Physics - Engineering Electromagnetics - Maxwell

Does anyone know any good lecture material online that I can learn this concept on Maxwell? It would be good if there is a video webcast on this concept. I am having some problem understanding this chapter.
48. ### Need help understanding electromagnetics and relativity

Hello I'm having a little trouble understanding how two observers in two different inertial frames of reference would view the same simple electromagnetic event. Let's call the first frame K, and we can use cartesian coordinates x, y, z, and t for time in K. There is an electric field E in K...
49. ### Electromagnetics in Spherical Symmetric Problem

In a spherical symmetric problem the only nonzero components of the electric and the magnetic field are Er and Br Why?
50. ### Calculating electrostatic potential energy

Homework Statement Consider potential field V(ρ, φ, z) = V_0/ρ in free space and cylindrical coordinates. Calculate electrostatic potential energy stored in half cylindrical shell defined by a≤ρ≤b, 0≤φ≤π and 0≤z≤h. Homework Equations W_E=½∫∫∫ρ_vVdV The Attempt at a Solution I have no idea...