The classical theory of electric and magnetic fields, both in the static and dynamic case. Also covers general questions about magnets, electric attraction/repulsion etc. Distinct from electrical-engineering.

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With the help of a given charge is it possible to obtain a charge many times greater in magnitude

Consider a spherically conducting sphere. If a charge(say positive) is placed near the sphere, then it will lead to separation of charges inside the sphere.My question is, can we create charges more ...
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27 views

Attraction between electromagnet and a permanent magnet - at which point is the force the strongest?

You have an air-core inductor with current applied, so that the magnet in the picture will be attracted to it. At what position will the force between the two be the strongest and at which the ...
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16 views

Wigner-Eckart theorem and Van Vleck paramagnetism

Using the Wigner-Eckart theorem, we can express the matrix elements of Langevin's paramagnetic Hamiltonian $L_z + g_S S_z$ using only the quantum numbers of the total angular momentum, $J$ and $m_J$, ...
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19 views

What is a simple model to find the jump height for the Thomson's Jumping Ring experiment?

I'm trying to devise a basic formula that could give a rough estimate for the jump height reached in the Thomson's Jumping Ring experiment, as detailed here. However, it's pretty difficult as most ...
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39 views

Can a circuit produce a magnetic force on itself?

Well I think that it is kind of obvious, because the magnetic force does not specify if the fiel is produced or not by the circuit that feels it, but I had never heard about "autoinduced forces" or ...
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43 views

Electromagnetic Tensor under Lorentz transformation, $F'(\Lambda x)= \Lambda F(x) \Lambda^T$?)

Suppose we have a configuration of electric and magnetic fields $E(x1,x2,x3,x4)$ and $B(x1,x2,x3,x4)$, they depend of position and time for a fixed coordinate system. And I want to know how someone in ...
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17 views

Energy density inside anisotropic materials

I'm taking some college courses on electromagnetism and there was some talk of energy stored by electromagnetic field and its density. The expression that we use to calculate energy density stored by ...
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21 views

Electro magnet strength to weight ratio

I was wondering. How would I work out how strong a magnet would have to be to support my weight.
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24 views

Is frictional heat just electromagnetic interactions creating infrared radiation?

Example: Rub your index finger on a sheet of paper and you will feel that it will get noticeably hotter Is the reason you feel this increase in heat (technically an increase in kinetic energy of the ...
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23 views

How do Hertzian dipoles relate to reflection of EM waves?

We recently performed an experiment where the intensity of microwave radiation reflected off different materials was measured. A comment in the script noted that the mechanism by which reflection of ...
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31 views

Turning a k-space integral into an energy integral for a conductivity tensor

Looking over a derivation of the conductivity tensor for magneto-resistance, I got stuck trying to go from (1.133) to (1.134), transforming the k-space integral into one over energy. In this ...
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14 views

Transformer core area

I want to ask you people that where does this formula ca = 1.152 ×√ (output voltage × output current) I am keen to know about 1.152 factor and amaze to see that how vs and is are reslonsible for max ...
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23 views

multipole moments of dipole with finite spacing

Can a dipole with finite spacing between poles be represented by pure multipoles centered at the origin? Say for example that I have a dipole with finite spacing $2\epsilon$ between the poles. I ...
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10 views

Physical interpretation of Robin's boundary conditions for Poisson equation

i want to know the physical interpretation of Robin's boundary conditions for Poisson equation on $\Omega=]0,a[$x$]0,b[$ $-\Delta u =f $ and $\frac{\partial u}{\partial n}+\alpha u =g $ on ...
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14 views

(Induced) Surface charge/current density of dielectric material?

Consider an incident $s$-wave traveling from vacuum to a linear dielectric material (at an angle), clearly there's no surface charge density since $\vec{E}$ has no normal component. However, we can ...
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20 views

Feasiblity of a long spinning top using an electromagnet to pull on Earth's magnetic field

Would it be feasible to build a infinitely spinning top (ref. Inception) by including a battery powered electromagnet who's polarity flipped in sync with the top's rotation such that the pull against ...
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42 views

Current induced in concentric superconducting loops

Suppose you have two superconducting loops, concentric, in a plane. Also suppose that their radii, $R_1$ (outer) and $R_2$ (inner) have the same order of magnitude (so you can't assume $B$ through the ...
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26 views

Good textbooks on nonlinear electrodynamics?

Looking for suggestions for a good textbook on nonlinear electrodynamics, not going into optics immediately as most textbooks tend to do but perhaps a rigorous mathematical exposition on the ...
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Relating noise spectral densities of magnetic flux and voltage

My problem is as follows. I generate a voltage $V$. This voltage is applied to a resistor R, producing a current $I$. This current is then passed through a superconducting coil, producing a magnetic ...
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40 views

Change in energy eigenvalue of Schrödigner-Pauli equation

If I apply a uniform magnetic field to a paramagnetic material, I will re-orient the quantum spins of the electrons on the atoms to create a net magnetic dipole moment. When the re-orientation occurs ...
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272 views

Relation between intensity of light and amplitude of electric field?

A question in my textbook involve finding the electric field amplitude at a point in space given the intensity of light. It uses the following equation to solve it: - ...
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24 views

How will EM waves behave if they are made to pass through a region of intense magnetic/ electric field?

My question is exactly what the title says. I think they should not be affected as photons are uncharged. But shouldn't the oscillating Electric and Magnetic fields be affected by the electric/ ...
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40 views

Electric Field From a point P

A rod of length $L$ and total charge $Q$ creates an electric field at a point $P$, $x$ units away. We need the electric field at this point. I am working on a physics problem for homework and the set ...
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23 views

What causes that the outer electrons of iron have the same spin and creates a dipool?

Iron has the capability of magnetism. The cause of that is that the spins of electrons in the outer shell are the same so they pushes each other away because of Pauli exclusion principle so they are ...
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25 views

how would an iron encapsulated electromagnet work?

I have been searching for this for a while now, but, a normal electromagnet works with(example) an iron cylinder and a copper coil around it, but would it work the same if you were to encapsulate it ...
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61 views

Relationship between the g-factor and the gyromagnetic ratio?

From what I have read the g-factor and the gyromagnetic ratio are two different quantities. It appears to me that the gyromagnetic ratio is the ratio between (any) angular momentum and the magnetic ...
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38 views

What does this coordinate transformation in the Wave equation mean?

My tutor derived the following of which I do not understand the transformations (2.1) and (2.2): $$\Delta\vec{E} - \frac{1}{c^{2}} \frac{\partial^{2}\vec{E}}{\partial t^{2}} = \frac{4\pi}{c^{2}} ...
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46 views

Radius of solenoid on the magnitude of magnetic field

I'm working on a project and have made a solenoid. I want to know the effective parameters on the magnitude of the magnetic field. $$B=μNi$$ In this equation, the radius of the solenoid don't have any ...
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57 views

Landau levels in uniform magnetic field

Intro Landau levels are obtained by gauging the vector potential to be $$ \vec{A}=\left(-By,0,0\right) $$ By which the Hamiltonian: $$ H={1\over 2m}\left(\vec{p}-q\vec{A}\right)^2 $$ can be ...
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28 views

Charged rotating sphere in Maxwell-ChernSimons theory

Does anybody know what the electromagnetic field of a charged rotating sphere in five dimensional Maxwell-Chern-Simons theory is? This theory has action \begin{equation*} S = - \frac{1}{4} \int d^5 ...
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35 views

Magnetic field of one electron

I want to reproduce a calculation of the magnetic field at the atomic nuclei produced by one electron in hydrogen: Maxwell gives us: $\vec \nabla \times \vec B = \mu_0 \vec j$ Doing the surface ...
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32 views

Surface bound charge density in dielectric displacement

In Griffiths, it derived that the electric potential caused by Polarization $\bf {P}$ is written $$V({\bf r}) = \frac{1}{4\pi \epsilon_0} \int_{\mathcal{V}} \frac{\hat{\gamma} \cdot {\bf P}{({\bf ...
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Magnetic Field Flux Density Disambiguation

The Electric Field is defined as the electric force exerted on a positive test particle: $$\vec{E}=\frac{\vec{F}}{q}$$ The Electric Flux is defined as: $$\Phi=\iint \vec{E}\cdot \vec{dS}$$ The ...
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34 views

Superconductors and hoverboards

We know that superconductors are repelled by magnetic fields. The earth has a magnetic field of about $10^{-5}$ Tesla. I just want to know if it is possible to use this property of earth to make ...
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13 views

What is the direction of area vector while calculating flux in AC generators?

I was told that in case of an open surface, the direction of area vector is considered to be in the direction of magnetic field but my doubt is won't the direction of area vector change as armature ...
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25 views

What's “the” physical explanation of hysteresis in ferrimagnetic materials?

I am wondering what is "the" or "a" physical explanation of hysteresis in ferrimagnetic materials. From what I've read in wikipedia and Cullity's book, there is a simple physical explanation for ...
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Field line Direction and exerted force

Magnetic field lines of a magnetic field have different directions. What information about the force exerted on a charge will give us the direction of field lines?
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28 views

(boundary conditions) Interface between two lossless media

I'm wondering why there's usually no free charges nor free currents in the interface between two lossless media? no free current "I guess" is due to the insulating nature of a lossless media but why ...
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54 views

induced current in loop

I'm re-asking this question that was posted by @zhzh and subsequently closed. If you have a loop that is spun clockwise as a magnet is moved near it, is a current induced in that loop? If the ...
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21 views

Does the form of a hysteresis curve depend on the magnetic field change rate?

I have given some people access to a Monte Carlo program that I created to simulate ferrofluids. They adapted it in order to simulate hysteresis loops. I had warned that Metropolis algorithm can only ...
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64 views

Simple Explanation of Kondo Effect

Does anyone have a simple explanation of the Kondo Effect? (i.e. a simple physical picture + maybe equations to think of?) My current understanding is this: If we consider an electron scattering ...
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20 views

Time dependance of oscillating sheet of charge

I am working on a practice problem involving maxwells equations. We have an infinite sheet of charge density $\sigma$ in the x-y plane and it is oscillating as x= $\Re [x_0e^{-i\omega t}]$. I want to ...
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22 views

influence of soft iron in magnetic lenses

I'm currently working as an intern in a research group which is specialized in transmission electron microscopes. I'm reading a book from David B. Williams and C. Barry Carter : Transmission electron ...
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27 views

Relationship between magnetic force acted upon a diamagnetic substance and the magnetic field applied to it

I have a sample of bismuth that I have applied a measured B-field to through the use of a solenoid electromagnet. I've been trying to find a formula relating the B-field to the force that the bismuth ...
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29 views

Light reflecting off a sphere

Suppose light of momentum $-P\hat{\textbf{k}}$ is shone on a sphere. What is the momentum transferred onto the sphere? I think the transferred momentum upon reflection is given by ...
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22 views

The frequency induced by the alternating current

Let set up the experiment as followed. A string is stretched at two ends. Two magnet poles N and S are placed under and above the string. Now we let an alternating current go through the string with ...
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61 views

Response function in plasma

I am reading an article where authors investigate how a particular type of electrostatic waves propagates in a plasma. They start with the Poisson's equation in the next form: $$\nabla^2 ...
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62 views

Problem in computing self-induction for a wire with zero diameter

This is quoted form Edward Purcell's Electricity and Magnetism; it tells about the problem of computing magnetic flux during self-induction for a wire with zero-diameter: You may think that one of ...
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Increase Phase Velocity by Losing Power

I just read some words from the book Optical Waveguide Theory by Snyder, Allan W., p226. It says that However, although it is possible for the phase velocity of a mode to exceed the maximum speed ...
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What's the analogy of a single photon from the perspective of “classical electromagnetic wave”?

I guess there isn't an accurate analogy. But what is the best analogy we can use? It seems an idea sinusoidal wave of a single frequency doesn't fit as a photon at all. In a certain sense, at least ...