Read about elecrtomagnetism | 112 Discussions | Page 1

  1. Assassinos

    I Does moving an insulating cylinder produce a magnetic field?

    Suppose that we have an insulating cylinder with ##\rho_q##. If i move the cylinder towards ##+\hat{n}##, will it produce a magnetic field? My assumption is that since we have an insulator, then the electrons are bound and there cannot be a current, thus a magnetic field is not produced. Also...
  2. U

    I Stratton-Chu solution, special case

    I will try to ask the question, saving as much calculations as possible, so as not to weigh down those who want to try to help me. Starting from the general electromagnetic problem in empty space, taken as a domain a volume V delimited by a closed surface S, Elliot (1) shows how the field (i.e...
  3. L

    Electromagnetic plane waves from a current sheet

    I have an infinite sheet (in lossless, homogeneous medium) of time-harmonic current in ##yz##-plane at ##x=−d##. The current density on this sheet is given by $$\mathbf{J}=\hat{z}J_0\delta(x+d)$$ ##δ(x+d)## is delta function. Moreover, there is a perfect electric conductor (PEC) half space at...
  4. K

    B How a Secondary Resistor affects the Transformer Primary Side?

    Let's assume a 2:1 transformer which has a 100V Source connected on the primary circuit and has no/negligible resistance, on the secondary circuit a 5 Ohms resistor is connected. Using the 'Impedance Transfer/Reflection' method, the primary circuit would act as if there was a 25 Ohms resistor...
  5. Zack K

    Potential difference in a 2 disk system (Capacitor)

    Homework Statement A capacitor consists of two large metal disks placed a distance ##s## apart. The radius of each disk is R ## (R \gg s)## and the thickness of each disk is ##t##. The disk on the left has a net charge of ##+Q## and the disk on the right has a net charge of ##-Q##. Calculate...
  6. olgerm

    I Moving charges in a moving frame of reference

    Hi. If 2 bodies with charge q are in rest then both have electric force ##F_1=\frac{q*q*k_q}{|\vec{r}|^2}##. But in another frame of reference, that is moving with velocity v relative to first frame of reference, they feel both magnetic and electric force...
  7. majormuss

    Finding the electrostatic potential of a square sheet.

    Homework Statement Consider a uniform surface charge density σ on a square of unit area. (a) Compute the electrostatic potential Φ along the line normal to the center of the square. My current attempt at a solution (image attached) is either incomplete or is simply wrong but I am unable to...
  8. Mohammad Fajar

    I Electromagnetic Field vs Electromagnetic Wave

    When there is electric charge, then there is an electric field in space aorund it. Or when the electric charge is moving (without acceleration), then it is produced magnetic field in a space around it. Both of these fields permeated to infinity according to Maxwell theory. But how fast...
  9. Hans de Vries

    A New Covariant QED representation of the E.M. field

    90 years have gone by since P.A.M. Dirac published his equation in 1928. Some of its most basic consequences however are only discovered just now. (At least I have never encountered this before). We present the Covariant QED representation of the Electromagnetic field. 1 - Definition of the...
  10. tworitdash

    Classical Which classic book to follow for Advanced EM?

    The book should have the following content. I want to refer a classic book which explains every detail. 1) Ohmic losses at high frequencies 2) Potentials and Green's functions 3) Image theorem 4) Fields radiated by sources in the far field region 5) Equivalence and reciprocity theorems 6)...
  11. B

    Electric field of "half" an infinite charged sheet

    Homework Statement A charged sheet with charge density ##\sigma## is described by ##-\infty<x<0,-\infty<y<\infty, z = 0##. Find the electric field at ##(0,0,z)##. Homework Equations Electric field of continuous density charged body from the Coulomb law: $$E = \frac{1}{4\pi...
  12. G

    Mutual inductance coefficient with so little info

    Homework Statement I have the following circuit: The two inductors are connected in series are characterized by internal resistances R1 and R2 and self-inductances L11 and L22. The magnetic coupling factor between the inductors is k = 0.75. The inductors carry the same current i. What is...
  13. tworitdash

    I Why different cutoff frequencies for TE and TM in a medium?

    Today in my electro-magnetics class, we were told that the cut-off frequencies of TE and TM waves on a co-axial cable are different. As far as I understand, it says that if there is an electric field with one frequency projected on it and if we know that the problem can be simplified if we see...
  14. P

    I How was this formula derived? (Electromagnetic)

    I recently learnt about Electric displacement field and capacitors, and I have a question that how was the formula derived shown below (blue circle part)? Thanks!
  15. S

    Electric displacement field

    Hello, I'm going through electrodynamics by griffiths.. I'm unable to understand the case 1) for no free charge and 2)when curl of P(polarisation ) is zero at the boundary Then what can we comment about D the displacement field having both it's divergence and curl zero at the boundary. Please...
  16. I

    I Magnetic field created by a current carrying wire

    Hi, I studied the Maxwell laws and the Biot Savart law and I found something I cannot answer. If you have a finite wire carrying current (let say 5m long) and you want to determine the magnetic induction vector due to it at some point that has distance r from the wire, you have 2 options I...
  17. M

    I Maxwell equation are derived in which coordinate system

    Ignoring special relativity theory,maxwell equation are deduced in which coordinate system?In most electrodynamics textbook,maxwell equation are deduced without specifying which coordinate we are using.For example,when we are solving poisson equation in static case,it seems we can freely choose...
  18. V

    A How are curvature and field strength exactly the same?

    I am watching these lecture series by Fredric Schuller. [Curvature and torsion on principal bundles - Lec 24 - Frederic Schuller][1] @minute 34:00 In this part he discusses the Lie algebra valued one and two forms on the principal bundle that are pulled back to the base manifold. He shows...
  19. WeiShan Ng

    Find angular momentum of EM field in terms of q and ##\Phi##

    Homework Statement A point charge q sits at the origin. A magnetic field ##\mathbf{B} (\mathbf{r})=B(x,y)\mathbf{\hat{z}}## fills all of space. The problem asks us to write down an expression for the total electromagnetic field angular momentum ##\bf{L_{EM}}##, in terms of q and the magnetic...
  20. S

    Electromagnetism homework check

    Hello. I have an assignment to submit and I really want to get full marks/know where I went wrong If anyone has a tiny bit of free time would you mind please checking my homework? Even if you just check 1 page I will be so grateful. Thanks again https://imgur.com/a/rHVdjzn
  21. BookWei

    What is the second-order Born approximation?

    Homework Statement Equation (10.30) in Jackson is the first-order Born approximation. What is the second-order Born approximation? Homework Equations The Attempt at a Solution I can get the first-order Born approximation in Jackson's textbook. If I want to obtain the second-order (or n-th...
  22. B

    Polarizibility, Electric Field & Force

    Homework Statement A neutral atom with known polarizability α is located at the origin. A point charge Q is situated on the y-axis a large distance d from the atom. (The atom therefore becomes polarized due to the electric field of the point charge.) (a) Find the electric field due to the atom...
  23. A

    Verification of Ampere-Maxwell Law

    Homework Statement A current I flows along a wire toward a point charge, causing the charge to increase with time. Consider a spherical surface S centred at the charge, with a tiny hole where the wire is – see figure below. The circumference C of this hole is the boundary of the surface S...
  24. G

    I Can Gauss' Law be used to calculate the electric field generated by a uniformly charged thread?

    Hello, Can not Gauss's Law be used to calculate the electric field generated by a uniformly charged finite thread? I suppose it is because I can not consider the electric field constant (always going to the same direction), and for this I would have to do it by parts (the lateral flow, and the...
  25. G

    I Counterexample to the Poynting theorem

    The counter-example is as follows: We have a rectangular toroid ferrite(ring ferrite), magnetized in a closed loop around the ring. We put capacitor plates on top and bottom surfaces, with suitable direction. Now the Poynting vector points inwards or outwards. We look at a cylindrical surface...
  26. A

    Equivalent point charge, dipole, and quadrupole

    There is a big sphere with charges distributed on the surface. N charges are distributed on a patch of the sphere (all the information of the charges such as their locations are known). Suppose the rest of the sphere has similar charge distribution as the patch, how to approximately calculate...
  27. R

    Does r=mv/Bq hold true considering Maxwell's E.M wave theory?

    Homework Statement : [/B]This is a general conceptual doubt, not a numerical based doubt. We were taught that when an electron(or any charged particle) moving with uniform velocity enters a magnetic field(perpendicular to its direction of motion), then a force acts on the electron which makes it...
  28. M

    Distribution of ions in a cylindrical container

    Homework Statement In a cylindrical container of radius ## R ## and height ## h \ll R ##, with long axis ## \hat{z} ##, in the presence of gravity acceleration ## \vec{g} = - g \vec{z} ## is contained a neutral ionized gas, whose ions can be described as material points with electric charge ##...
  29. S

    I How an electric field is absorbed by a dielectric

    when a em waves strikes a dielectric the atoms vibrate in response to the electric field and if the frequency matches the resonant frequency the Lorentz oscillator the electric field is absorbed how a field can be absorbed we know the em field contain energy how is the em field destroyed is some...
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