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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22 views

Are electric and earth's magnet fields can travel parallel to one another? [closed]

or Can we able to pass an electric field along with earth's magnetic field ? I'm looking to create anti gravity over the fields even my thought is silly, I want to create a hover boat to fly in the ...
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20 views

Effective medium approaches - Volume averaging vs homogenization?

In dealing with multiphase two phase systems as an effective medium there are two approaches that can be taken. Volume averaging and homogenization. Volume averaging is very intuitive, just take ...
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43 views

Difficult induced current problem [closed]

consider the following setup shown below in the diagram. A circular conducting ring is placed in a increasing magnetic field into the page.Points $A$ and $B$ contain two bulbs. Initially both are ...
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1answer
32 views

Why are there no charges inside a conducting sphere?

Why is it necessarily true that all charges occupy themselves only on the surface of a conducting sphere, and not anywhere inside the sphere? One argument is that if a charge were to be inside a ...
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42 views

Experimental evidence for nonlinear electrodynamics

Has any experiment been conducted which shows that, above a certain threshold of field strength, electromagnetic interactions become nonlinear? If not, which field strength threshold is the one under ...
3
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1answer
57 views

What is the gauge group of eletromagnetism?

Gauge transformations allowed by physical theories form groups. For example, a wave function in quantum mechanics can be multiplies by $e^{i\theta}$ and this won't change a thing. So the gauge group ...
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40 views

Through what potential difference would an electron need to be accelerated for it to achieve a speed of 28.0% of the speed of light [closed]

Through what potential difference would an electron need to be accelerated for it to achieve a speed of 28.0% of the speed of light, starting from rest? So Initial speed = 0 Final speed = .28C So ΔU ...
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1answer
35 views

$\mathbf{J}$ and $\mathbf{E}$ having the same direction [closed]

Ohm's Law States that $\mathbf{J} = σ\mathbf{E}$ this implies then that $\mathbf{J}$ and $\mathbf{E}$ have the same direction . But we know that $\mathbf{E}$ in normal to a conductor and $\mathbf{J}$ ...
3
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2answers
94 views

Does light interact with electric fields?

We know that light is an electromagnetic wave and it does interact with charges. It contains magnetic field and electric field oscillating perpendicularly but when we apply an electric or magnetic ...
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30 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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1answer
32 views

behavior of dissolved ionic compounds in an electric field

Consider the following setup - An open, insulating box is filled with distilled water, into which is dissolved a significant amount of pure NaCl. Two insulated lumps of conductor, one with a large ...
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2answers
51 views

Negatively charged ball orbiting positively charged ball in space?

Would it be possible to make something like two metal balls, one positively charged and one negatively charged, in space, where the negatively charged ball would orbit the positively charged one like ...
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26 views

Calculating temperature in a steel rod/bar which is heated by induction?

I'd like to calculate what kind of temperatures I could achieve in a steel (or copper) bar/rod with the help of heat induction from a coil. Firstly, let's not take radiation or convection into ...
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20 views

Books on Spectral Jacobian

Can anyone point me a book to better understand "spectral Jacobian". I am studying X-parameters, I have the book X-Parameters: Characterization, Modeling, and Design of Nonlinear RF and Microwave ...
2
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0answers
46 views

Do divergence and curl of Lorentz force have some physical meaning?

Time ago I started thinking about this: if we take the well known Lorentz Force expression, namely $$\mathbf{F} = q\left(\mathbf{E} + \mathbf{v}\times\mathbf{B}\right)$$ and we operate $\nabla\cdot ...
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2answers
39 views
0
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41 views

A question in electrostatics

The following is from Problems and Solutions on Electromagnetism. The electrostatic potential at a point $P$ due to an idealized dipole layer of moment per unit area $\pmb {\tau}$ on surface ...
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1answer
37 views

How can we verify the direction of electric displacement is radial?

I have two questions about electric displacement $D$. The following is a problem in Griffiths. A long straight wire, carrying uniform line charge $\lambda$, is surrounded by rubber ...
1
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1answer
34 views

Why is there no electric potential energy when it is directly above an electric dipole?

If you have two opposite charges of equal magnitude, why is the potential energy of another random particle that is directly above or below the middle distance between the two charges have 0 electric ...
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0answers
24 views

What are the differences between an EM wave propagating in a conductor and an electrical impulse traveling down a conductor?

I'm afraid I don't quite understand the fundamental and mathematical differences between a propagating electrical signal in a conductor and an EM wave traveling in a conductor. Situation: I found ...
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0answers
25 views

On Rayleigh-Jeans black body distribution derivation

When trying to derive the Rayleigh-Jeans distribution function, all authors say that in k-space each solution of the electromagnetic wave functions(of waves inside a cubic black body) represents an ...
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0answers
12 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 ...
4
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0answers
50 views

Maxwell Equations don't give unique Electric Field?

Consider the class of electric fields given by $$\mathbf{E}=\begin{cases} \ln (Cr)\hat{z} & 0\leq r < R\\ 0 & r> R \end{cases}$$ where $C$ is a constant and $r$ is the polar-distance ...
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2answers
43 views

What is meant by “current” in this context?

This is a quote from Optics by Hecht: A stationary charge has a constant E-field, no B-field, and hence produces no radiation—where would the energy come from if it did? A uniformly moving ...
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19 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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0answers
12 views

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?
3
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2answers
64 views

How can I use a magnet to lift a paperclip?

This question has been asked already, but no satisfying answer came up. All the answers seem to push the problem further, but do not explain clearly what is going on. I will reformulate it for a ...
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0answers
11 views

Force on a magnetic dipole due to a magnetic field

Imagine a solenoid which has current $i$ and is producing a magnetic field $B$ which equals $$B=\mu N i$$ Now, imagine we put a small cylindrical magnet at the end of the solenoid. Then because at ...
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24 views

Series expansion of potential due to a dipole displaced from the origin

I learn that we can expand the electric potential in an infinite series of $\rho$ and $\cos(n \phi)$ when solving the Laplace equation in polar coordinates. The problem I want to consider is the ...
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44 views

Where to place a charge to establish net force of 0? [closed]

A charge, Q2 = -15.00x10^-6 C, is 10.00 cm to the right of charge Q1 = 18.00x10^-6 C. Where can a third charge be placed, along the line connecting Q1 and Q2, such that it experiences no net force ...
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14 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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0answers
21 views

Force Exerting on a magnetic train

A question is already asked ( How does this “simple” electric train work? ). But I've got a question about it. In order to calculate the force which is being exerted on the system including magnets ...
3
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1answer
36 views

Analogue of charge for magnetic fields?

Now, I understand how there are no magnetic monopoles, and hence no analogue of magnetic charge in terms of a scalar field, but is there a similar concept that instead uses a vector or spinor field to ...
0
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1answer
31 views

Does the electromagnetic force “split” at lower than normal energies?

Since we have working models for forces "combining" or being describable via a single framework at higher energies (such as the "electroweak" force and the aim of GUTs), does electromagnetism split ...
4
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62 views

How can one confirm creation of magnetic graphene?

Recently my high school physics teacher contacted me looking for an expert to ask about this situation. I am paraphrasing his correspondence below: I just had a a student accidentally create ...
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33 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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0answers
20 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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0answers
62 views

Would a grid of $10^{57}$ hydrogen atoms collapse?

Assume we have a gridded cube of $10^{57}$ hydrogen atoms, with all atoms 1mm apart from other atoms. This 'cube cloud' is in an area of space that would otherwise be at zero g, were it not for the ...
1
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1answer
53 views

if there is no electric field then any charge exists or not? [closed]

If we assume a region of space in which there is no electric field, can we say that no electric charge exists? I think that there is no electric charge particles to create electric field for this ...
0
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1answer
52 views

Was decoupling actually detripling?

As I previously understood it, before recombination, high energy photons were bound up in interactions with excited electrons, meaning electrons couldn't settle into orbit with protons and other ...
1
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1answer
32 views

Cold Atom Hot Atom 2: Minerals Attracted to Heat

In electric hot water tanks why do calcium quickly form on the heating elements? I watched some one put in a new element. An hour later it stops working. Just to check he took the element and it had ...
1
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1answer
36 views

Why don't simple circuits cause the electrical breakdown of air surrounding them?

Electrical breakdown of air occurs when the electric field exerted by a charged object exceeds the electrical breakdown limit of air which is $3.10^6 V/m$. Since even 1 Coulomb of charge can exert an ...
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0answers
23 views

Magnetic Forces and Junkyard Magnets: What's Going On? [duplicate]

In my electromagnetic theory class, I learned that magnetic forces do no work. This is easy to see when observing a cyclotron; the speed never changes, so the kinetic energy never changes and ...
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0answers
60 views

Limitations on the use of Ampere's Law

I have tried to find a thread with an answer to my question but have not been able to do so. Suppose that you are asked to find the B-field due to a finite length of straight current carrying ...
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0answers
56 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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0answers
15 views

EM Radiations, wavelength and Wein's Law of Displacement [duplicate]

Why can black bodies emit all wavelength radiations? Also, in Wein's law of displacement, how do we sat that wavelength corresponding to the max intensity of the radiation is inversely proportional ...
0
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0answers
29 views

Electric Field at a point some distance above a uniformly charged cylinder

In this problem I am trying to solve, I am trying to find the electric field at a point directly above a uniformly charged cylinder. The cylinder is oriented so that the two round face are parallel ...
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3answers
43 views

How does one apply Gauss's Law when dealing with two infinite planes?

If you have two parallel planes with one density of 1 C/m^2 and the other with -1 C/m^2 density and you need to find the electric field at a point in the middle, how do you use Gauss's Law? I drew a ...
2
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1answer
69 views

What symmetry gives you charge conservation?

This is a popular question on this site but I haven't found the answer I'm looking for in other questions. It is often stated that charge conservation in electromagnetism is a consequence of local ...
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16 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 ...