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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74 views

In terms of the Ampere-Maxwell law, why is $\vec {E}=0$ in a wire of a capacitor circuit?

I'm currently studying from "Introduction to Electromagnetics" by D.J. Griffiths. In the book the significance of the displacement current term is explained by looking a non-steady capacitor circuit ...
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1answer
35 views

Eddy currents on a conductors surface, and induced current flow in a circuit coexist?

The title seems confusing, because Eddy currents are induced currents... however, let me explain. Assume the following closed loop passing a uniform magnetic field like so: Now, this loop would ...
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0answers
36 views

How to achieve vertical lift using magnets [duplicate]

Is there a way to create vertical lift using magnets which are aligned with same facing polarity?
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1answer
245 views

Calculating the magnetic field from rectangular conductor?

I want to apply the Biot-Savart law to calculate the magnetic field at a point created by current flowing through a square/rectangular conductor. More specifically, a trace on a printed circuit board. ...
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0answers
42 views

How to model radio wave attenuation by seawater?

From the very limited literature I can find regarding radio waves in saline-water solutions (as in seawater), I have been able to find very few corroborating models of radio wave propagation through ...
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1answer
32 views

Can light (electromagnetic radiation) cause electromagnetic induction in a wire?

Can light, as an electromagnetic wave, cause electromagnetic induction in a wire by passing near the wire? Does a moving electromagnetic wave cause a varying magnetic field in the region near the ...
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2answers
390 views

How is the current flow perpendicular to the wire?

This answer gives a great explanation of how surface charge builds up to force the current to move perpendicular to the wire: http://physics.stackexchange.com/a/102936/41086 However, it fails to ...
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1answer
21 views

EMF Induced in a solenoid

When is the emf induced in a solenoid higher,when making or breaking the circuit? Isn't it the same magnitude since change in flux is same in both rhe cases?
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1answer
39 views

Will this system of magnets rotate?

A system of four magnets are placed as shown in the figure. As per the application of Maglev, a stationary magnet produces electro motive force with the magnets in motion. Note That the point O is ...
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2answers
131 views

Induced EMF, additive to conductor's closed circuit?

Assume the following conductor, with current flowing, powered from a source $S$: Now, I've introduced a magnetic field($B) to the conductor covering a small area of it like so: The change in ...
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2answers
2k views

Magnetic field lines

When I searched the net about magnetic field lines, Wikipedia told something about contour lines and that magnetic materials placed along a magnetic field has some specific loci, which i did not ...
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2answers
462 views

Is Newton's third compatible with retarded Lorentz force?

In Griffiths Introduction to electrodynamics it is said that Newton's third law is not valid in electrodynamics, but, in the example given, the it does not consider the retarded values for the fields ...
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0answers
19 views

Single slit diffraction treated as a differential equation

I want to find the values of electromagnetic fields that result from single slit diffraction. This should be possible by solving maxwell's equations for appropriate boundary conditions. But I'm not ...
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1answer
75 views

Can a train with magnets attached move with less fuel?

For a train, if we attach magnets ( big ones ) such that, for each compartment north faces front and south faces back, can that train move. So if this is right, we can move a train by just moving the ...
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3answers
273 views

Electromagnetism boundary condition

The dielectric slab surrounded by air as shown in diagram has permittivity $\epsilon$ different from air and permeability almost same as air. Electric field everywhere within the slab is given to be ...
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2answers
127 views

How come the length of a wire does not affects on the circuit current?

Today we started learning about the electromagnetic induction. Out teacher gave us the following explanation: Suppose we have a conduction frame inside a magnetic field $\vec{B}$ going towards the ...
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2answers
35 views

Electric Potential Between Two Like Charges

At the point horizontally across and equidistant from the centers of the two charges (also oriented horizontally), what is the electric potential? At that point, the electric field of the first charge ...
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0answers
24 views

How does the hendo hoverboard achieve omni-directional movement?

An older thread already gave away the wonderful details of how the Hendo hoverboard achieves levitation, but how does it achieve its form of omni-directional control and movement? My idea was that ...
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1answer
53 views

Could a magnetic field repel electromagnetic waves?

If I understand magnetism correctly, then two magnetic fields with opposing directions would repel each other. Could this same affect happen to electromagnetic waves? And if so, could it be reproduced ...
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4answers
433 views

How do electrons actually move in a circuit?

Last year, we were taught about electricity, about how electrons move in a closed circuit. But as our teacher had not taught us about electric fields yet, she gave us a simplified model of motion of ...
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2answers
41 views

Do permanent magnets have an electric current surrounding them?

Permanent magnets seems to have different properties to electromagnets, such that electromagnets can be used for induction and energy transfer if a conductor is placed within their changing magnetic ...
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1answer
260 views

Boundary conditions on current carrying wire

I'm trying to simulate by finite elements method Maxwell equations for a current carrying wire. My 3d geometry consists of a cylinder and a box containing it. I will use a mixed formulation and ...
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3answers
102 views

Is this a Lorentz-scalar? How do I tell?

I'm struggling to identify whether a scalar is a Lorentz-scalar. E.g: $$\partial_i A^i \quad i \in {1,2,3}.$$ How do I determine if this is a Lorentz-scalar or not? If got the same problem with ...
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0answers
42 views

Are Landau levels always degenerate?

Solving the Landau problem, namely the quantum mechanical problem of a particle in a magnetic field leads to degenerate energy states, the famous Landau levels. My question consists of two parts. ...
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2answers
95 views

What kinds of behavioural anomalies can a zero-field-cooled (ZFC) / field-cooled (FC) split indicate?

If a material shows a spiltting in the ZFC and FC curves, is it necessarily superparamagnetic, or could there be any other reason for the irreversibility? I have heard spin glasses also show ZFC-FC ...
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2answers
208 views

Determining the minimum pull force of a magnet required to hold it in place

If I place a magnet on the underside of a metal object so that it is held there by its attraction to the metal, how can I determine the minimum pull force the magnet needs to have in order to keep it ...
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4answers
242 views

What is the *cause* of the Lorentz Force

Is it possible to explain what actually causes the force on a current carrying conductor in a magnetic field. I have read that this is due to the magnetic fields 'interacting' in some way. This ...
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1answer
59 views

Electromagnetic waves in detail

So I have read many things on electromagnetism and I have competed in the IPhO lf 2015, got an honorable mention. That is my level of physics. Now, I have been reading many topics again, this time ...
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1answer
49 views

Interpretation of a term in the Maxwell stress tensor

With no magnetism, the $xx$ component of the Maxwell stress tensor $T$ is $$T_{xx} = \frac{1}{2}(E_x^2 - E_y^2 - E_z^2)$$ I can see why there should be a $+E_x^2$ term, but intuitively I don't see why ...
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0answers
37 views

What is the electric field of a diffraction grating?

I'm trying to follow the equations in "Introduction to Modern Optics" by Fowles. He starts out with equation for a single slit of length $L$ and width $b$: $ U_p = C \int \int e^{ikr} dA $ where $U$ ...
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0answers
10 views

Wave propagation in 2D metal cavity

I would like to know there is an analytic solution for the propagation of electromagnetic waves in metals in a 2D case. The 1D case is well known to lead to a traveling wave with exponential decay ...
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3answers
947 views

why dosen't a charged particle radiate energy in circular motion in a uniform magnetic field?

I have studied in my Physics course that one of the drawbacks of Rutherford's atomic model was that when an electron will revolve around the nucleus, it is undergoing acceleration and so it should ...
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0answers
27 views

Motion of electrons in electric field

If an electron is allowed to pass through two parallel horizontal plates in a strong electric field such that the electron takes a parabolic path between the parallel plates. Will the electron stick ...
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0answers
28 views

What are some of the failed experiments to determine electron's position? [closed]

One that I could think of is trying to observe it with the help of electromagnetic radiation which could tear apart the atom. I asked this because I want to know what sort of methods are used to ...
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1answer
325 views

Magnetic fields in transformers and back emf?

i am having some trouble with understanding the magnetic fields inside transformers and how they relate to back emf. My first query is: is the magnetic field produced inside the soft iron core ...
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1answer
144 views

$U(1)$ 5-dimensional Kaluza-Klein topological defects

Five-dimensional Kaluza-Klein theory is well-known to predict that the electromagnetic field can be described as a curled additional dimension over four-dimensional spacetime. That is, you only need ...
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3answers
194 views

Energy-Momentum Tensor for Electromagnetism in Curved Space

$\newcommand{\l}{\mathcal L} \newcommand{\g}{\sqrt{-g}}$$\newcommand{\fdv}[2]{\frac{\delta #1}{\delta #2}}$I want to calculate the energy-momentum tensor in curved free space by functional ...
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1answer
87 views

What is the magnetic flux density “outside” the solenoid when AC current is passing through it?

I know that there are well defined equations explaining the magnetic flux density in the solenoid. However what about magnetic field outside the solenoid? How is the magnetic flux density related ...
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1answer
27 views

Connection between Polarization and Coherence in optics

It is not completely clear to me how the notions of polarization and coherence, in optics, work together! I quite understand both of them but it's still hard to grasp their deep connection. I'm quite ...
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2answers
200 views

Looking for lists of student difficulties with electromagnetism, circuits (DC and AC)

I'm trying to help with an Instructor's Guide for an introductory calc-based physics text, and it would really help if I could locate some lists of typical student difficulties with topics like ... ...
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1answer
60 views

Is EM interpreted in a principal or vector bundle?

I've read in a few places that EM is a $U(1)$-principal bundle; but is this correct? Isn't it rather an associated vector bundle using the adjoint representation of $U(1)$?
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1answer
141 views

Free Electromagnetic field in Lorenz gauge

To get rid of the extra term in the QED Lagrangian we need to redefine the electromagnetic four-vector: $A^{\mu} \rightarrow A^{\mu} - \frac{1}{c} \partial_{\mu} a(x)$ where $a(x)$ is the function ...
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2answers
92 views

Does special relativity explains working of an electromagnet?

I heard that special relativity could be used to explain the working of electromagnet, but couldn't dig anything out of it. Can somebody give some explanation of the above? I also heard that it is ...
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2answers
433 views

Electric field from current without Maxwell's law of induction

A long, straight wire carries a current that decreases linearly with time. What is the direction of the induced electric field outside the wire? I would interpret this as follows: a current ...
2
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1answer
84 views

Why does larger permittivity of a medium cause light to propagate slower?

I was wondering about what physically happens when light is transmitted through a non-magnetic medium. Specifically, I’m trying to visualize how materials slow down light as the electromagnetic wave ...
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0answers
1k views

Could Space Travel be achieved using a very strong magnetic field to warp space?

An Alcubierre Warp Drive could theoretically achieve faster than light space travel but requires exotic matter or negative energy to compress space in front of the spaceship and expand space behind ...
2
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1answer
121 views

Does the direction of the magnetic field inside a solenoid depends on the direction which it is turned?

Today trying to explain some magnetic stuff, just came across with a simple (at least seems) question. My question is brief: does the direction of the magnetic field inside a solenoid depends on the ...
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1answer
24 views

Co-ordinate rotations

I need help transforming a magnetic field vector from one co-ordinate system to another. I have the components of the Earth's magnetic field in a co-ordinate system with z facing radially into the ...
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1answer
37 views

Help understanding Diamagnetism

I need some help understanding Wikipedia description of diamagnetism https://en.m.wikipedia.org/wiki/Diamagnetism In the first sentence of the first paragraph, when said "...induced magnetic field ...
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0answers
21 views

Excitation spectrum of heisenberg model

I understand that ferromagnetic Heisenberg model (lattice of spin variables that can point in any direction) spectrum can be deduced by a $\lambda\phi^4$ theory with $\phi$ being complex. This model ...