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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$\mathbf{J}$ 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 $\mathbf{J}$ ...
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2answers
93 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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0answers
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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40 views

Show that the magnetic force is small compared to the electric force [closed]

Assuming the classical force ${\bf F} = e{\bf E} + e{\bf v \times B}$ acting on a charge $e$ in electric and magnetic fields $E$ and $B$, respectively, show that the magnetic force is small compared ...
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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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0answers
23 views

Books on Nikola Tesla [closed]

I'm looking for suggested books on Tesla. Preferably one that includes both biographical information as well as detailed descriptions of his theories/experiments/work.
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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 ...
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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
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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 ...
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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 ...
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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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0answers
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?
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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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0answers
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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0answers
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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0answers
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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20 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 ...
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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 ...
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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 ...
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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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0answers
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 ...
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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 ...
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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 ...
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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 ...
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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
59 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 ...
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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
68 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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0answers
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 ...
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1answer
35 views

Difference between reflection mechanisms in dielectric, metals and plasma

How the reflection and transmissions mechanism are different in metals, dielectric and plasma? I know that the density of free electrons is playing the role. Can anyone give an insight what is ...
3
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0answers
38 views

Why is the susceptibility $\chi(t)$ real?

So my question is quite simple I suppose, and perhaps trivial. It is known that the frequency domain susceptbility $\chi(\omega)$ is complex, and that the two parts can be related with the ...
1
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1answer
32 views

Can a magnet pick up heated iron filings?

I heard that heat can destroy magnetism (somehow randomize the electrons orientation and reduce the magnetism), but I like to know if magnetism could affect heated iron filings? (Here heated means ...
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1answer
36 views

Understanding of dipole moment and its vector property

I have a trouble understanding the electric dipole moment. The electric dipole moment formula is $${\bf p}= \int {\bf r}' \rho({\bf r}')d\tau '$$ I'm interested in the coordinate, the origin of which ...
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2answers
57 views

Why bar magnet can produce magnetic field?

Say I wrapped a piece of wire around an iron bar in a closed circuit connected to a DC power supply, the electrons starts flowing and moving charge produce magnetic field. Yet a bar magnet can produce ...