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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2answers
159 views

What is the difference between induced current and eddy current?

I was reading today about electromagnetic induction and eddy currents. But while reading I was unable to differentiate between induced current and eddy current. What is the difference?
0
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2answers
124 views

Who foots the (magnetic) energy bill?

Gravitational attraction and electrostatic attraction/repulsion are intrinsic properties of matter, any particle (electron, proton) for some unknown reason can produce KE at a distance. But magnetic ...
2
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2answers
46 views

Finding the direction of the magnetic force acting on a conducting wire

I have a problem in finding the direction of the force when a conducting wire is placed in a magnetic field. If I use Fleming's Right Hand rule I get a circular magnetic field, so what will be ...
0
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1answer
18 views

Torque due to a magnetic field

We have two infinite perpendicular wires, each carrying a current "i" and the distance between them is l. If both the wires are free to move, how will they arrange themselves because of the torque ...
4
votes
1answer
100 views

How do you go from quantum electrodynamics to Maxwell's equations?

I've read and heard that quantum electrodynamics is more fundamental than maxwells equations. How do you go from quantum electrodynamics to Maxwell's equations?
4
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2answers
123 views

When can I use $\wedge$ instead of curl?

It seems in some circles the wedge product is used in preference to curl. I have a basic understanding of Green and Stokes' formula, I wish to use the $\wedge$ notation from now on. Can someone tell ...
1
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0answers
12 views

Magnetic flux and flow of electrons

What does change in magnetic flux mean? How can you change magnetic flux? How does a change in magnetic flux influence a current of electrons (electricity)?
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2answers
34 views

Mass of magnet measured by weighing machine [on hold]

I put a magnet on a weighing machine, suppose it shows its mass. Part-1 of the problem: Now, I put another magnet on above this magnet so that it is repelled by the first magnet on the weighing ...
1
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3answers
78 views

How do charged particles interact?

You'll have to forgive me if this question is too wrapped up in "classical" thinking. I've read that electrons and protons interact by trading photons, but this only raises more questions. What ...
1
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1answer
71 views

Why there is a time gap between the news presenter and the field reporter?

This one has been in my mind for years, but I simply can not find any reason for this event. The Situation Imagine yourself sitting in the living room while watching television. It's 9 p.m and the ...
1
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1answer
28 views

Poynting vector plain wave

I'm calculating the poynting vector for a plain wave and I have some doubt. $$ \bar S = \frac 1 2 \bar E \times \bar H^* = ... = \frac {| \bar E|^2} {2 \zeta} \hat i_k $$ Now if I consider a ...
0
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2answers
22 views

Inductor Charging and Discharging

Why does the inductor discharges in the same path ( same direction of current ) as that of its charging unlike a capacitor which discharges in the direction opposite to its charging(current direction ...
2
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0answers
24 views

Momentum operator of a particle in an electromagnetic field

In quantum mechanics, to all observables correspond some self-adjoint operators. In the absence of an electromagnetic field the momentum operator is clearly $\vec{P}:=\frac{\hbar}{i}\vec{\nabla}$. ...
0
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0answers
17 views

What is the difference between primary and volume currents in electromagnetism?

What is the basic difference between the two currents and how each is contributing to the magnetic field at source and the surface?
6
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3answers
2k views

Can a third type of electrical charge exist?

Upon reading my book on physics, it mentions that there are only two discovered types of electric charges. I wonder if there could be a third type of elusive charge, and what type of effects could it ...
0
votes
1answer
13 views

what does “mode” means in Mode-Stirred Reverberation Chamber?

Recently I have been studying about properties of Mode-Stirred Reverberation Chamber (MSRC). I have run through some of the research papers about the MSRC, but none of them talks about the meaning of ...
0
votes
1answer
32 views

Junction conditions in GR including electromagnetism

I have recently learned about the Israel junction conditions in GR (as explained in for example Gravitation by MTW). I then tried to generalize it when including Electromagnetism, ie matching two ...
0
votes
1answer
36 views

Why does a green glass block more UVA/B rays than a blue one?

Why does a green glass block more UVA/B rays than a blue one? White glass blocks 36%, blu 43% and green glass blocks most UVA rays. That is why beer and olive oil bottles are green, they say. Edit: ...
3
votes
1answer
70 views

Why would a rotating charged sphere not have time varying electric field?

I have seen Gauss Law being used for a uniformly charged hollow sphere rotating with $\omega$. How is that valid to use Gauss law since it is an electrostatic law and if it is valid, why do we get a ...
0
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0answers
52 views

Thermal fluctuations in metals

My professor said that the $k_BT$ displacement in the energy levels of the band electrons is due to the space-thermal displacement of the potential of the ion host. I think that this displacement is ...
2
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1answer
68 views

an example where changing the frame of reference of an observer changes the outcome of events!

consider two identical charges moving with uniform velocity. There will be a magnetic force of attraction between them as two currents in the same direction attract each other. If I sit on one of the ...
4
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1answer
72 views

Why is optical orbital angular momentum (OAM) called “topological charge”?

The terminology "topological charge" is frequent in lots of research papers related to optical vortex or optical OAM, it is used to represent the optical OAM. Why? How to comprehend it?
2
votes
1answer
93 views

Angular momentum, what is it, is it conserved, and how do we know?

Firstly, most definitions of angular momentum assume a point about which you define angular momentum. I realize that you can consider the angular momentum about any point, and have many angular ...
1
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1answer
21 views

What does $E$ field look like around an inductor? What does $B$ field look like outside of a capacitor?

For whatever reason I could not find a picture of $E$ field around inductor, and also couldn't find a picture of $B$ field outside of a capacitor. The reason I think is because these quantities are ...
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0answers
16 views

What potential between charges leads to confinement

In (2+1)-d, instanton effect leads to a linear potential between charges. If we have two particles with opposite charges in this case, since linear potential diverges when the distance between the two ...
0
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0answers
25 views

My model of Conductors in “static” condition - Please analyze

My textbook presents an idealization of a conductor as made up of infinitesimal units of charge and derives results. I was not convinced, so I started thinking of how electric fields are in real ...
0
votes
1answer
18 views

The difference between EMR and lone Electric and Magnetic fields

I fail to understand the true difference between EMR and electric and magnetic fields. When current flows, there is an electric field due to the electron flow and a magnetic field, however no EMR ...
1
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1answer
41 views

image method to calculate the surface charge density on a conducting plate

There is a charge q at a perpendicular distance z = d from an infinite conducting plate z=0. We use the image method and place -q on the other side of the plate and calculate the field. This field ...
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1answer
25 views

Electric Potential of Conductors

I understand that charges in a conductor reside on the surface of a conductor. So why is it that the neutral inside of a conductor and the charged surface are at the same potential?
1
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1answer
38 views

What plane is Area in, in this equation?

I have the equation $$F = (NI)^2\mu_0\frac{\text{Area}}{2g^2}$$ Which calculates the force of an electromagnet. I was wondering if anyone knew what plane Area is taken from? I have heard it is the ...
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2answers
27 views

Electric Field in Conductor Zero?

My textbook claims that the electric field in a conductor is zero in a static condition, as otherwise, a current would flow. But what if I go infinitely close to a proton; there will be an electric ...
3
votes
0answers
60 views

Does Gravity Warp Coulomb's force?

Does gravity effect the "sphericalness" of the Coulomb force? For example, is the field 1 meter above a charge weaker than the field 1 meter below the charge? Could a 0.014% difference in the field ...
0
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2answers
46 views

Time reversal in Maxwell's electromagnetism [closed]

The statement of the time-reversal invariance of Maxwell's electromagnetism, as I understand it, is the following. Given $\mathbf{E}(\mathbf{r},t)$ and $\mathbf{B}(\mathbf{r},t)$ that satisfy all ...
0
votes
3answers
46 views

How can a glass rod become charged if it is an insulator?

I was reading some of the other questions, and I found this one about a glass rod and how it gains a net charge when rubbed with a silk scarf. I learned from working in a shop one summer that most ...
4
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0answers
51 views

Skin depth of current density in magnetic conductor at boundary between two different materials

Imagine a magnetic conductor with a cylindrical cross section, surrounded by a coil with a time varying current of $$I = I_0\cdot \cos (2\pi f t)$$ The conductor is split into two parts, the first ...
0
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1answer
32 views

Force of a solenoid on a ferromagnetic material

As I was trying to find an answer to another problem, I was informed that the equation I was using would not work. The equation I was using was $$F = (NI)^2\mu_0\frac{\text{Area}}{2g^2}$$ If this ...
0
votes
2answers
72 views

What is the electromagnetic field and what is the Higgs field?

I have several questions regarding the electromagnetic field and Higgs field which are connected, so I thought I would ask them together. Would be grateful for any information on any of the questions: ...
2
votes
1answer
32 views

Looking for a simple proof of symmetry of linear susceptibility tensor

Getting a diagonal susceptibility tensor: Define the linear susceptibility tensor as $\chi_{ij}$: $P_i = \epsilon_0\chi_{ij}E_j$, using standard notation for the electric field and the polarization. ...
2
votes
1answer
77 views

Is “scalar electromagnetics” real science?

This page claims that original Maxwell's equations, when formulated by Maxwell himself in quaternion form, had some special scalar part of electromagnetic field, which somehow appeared to describe ...
-1
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1answer
33 views

Direction of compass needle nearby an electric wire

Let through a straight wire flow an electric current. Using a compass needle how the needles tip will be directed to the wire? What happens when we switch the current direction and approach the needle ...
0
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0answers
36 views

Interaction Between Two Bar Magnets

How would one describe the interaction between two bar magnets? In the E&M course I took we described quite a few very basic electric interactions, but things that I would have thought of as being ...
-1
votes
3answers
30 views

Electromagnetic Theory [closed]

As, using the fact that E*A stays constant for a point charge ( E= electric field, A=area of sphere centered on charge touching the point where we have to measure E) , we can prove that E falls by ...
1
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0answers
48 views

Magnetic Force on a Ferromagenetic Material

I am currently working on a project involving solenoids, and I needed a force(Newtons, not a measure of magnetic field strength) equation. What I came up with after some digging around on the ...
1
vote
1answer
48 views

Coefficient matrix of quadratic Lagrangian

I've been studying path integrals from Weinbergs QToF vol 1. He says that when the $\mathcal{L_0}$ is quadratic in fields we can always write free term $I_0$ in the generalized quadratic form ...
0
votes
1answer
44 views

What physical forces allows for electromagnetic induction

In electromagnetic induction, what force is actually doing the work? what physical force actually drives the electrons around the circuit? Let's say we have a coil and an increasing magnetic field ...
17
votes
4answers
2k views

Are voltages discrete when we zoom in enough?

Voltages are often thought of as continuous physical quantities. I was wondering whether by zooming in a lot, they are discrete. I feel like the answer to the above question is yes as voltages in the ...
2
votes
1answer
44 views

Teflon and induction cookware

I remember once getting new Teflon (non-stick) cookware; however, when I tried this new cookware on my induction cooker the cookware did not heat up. My regular steel cookware worked just fine on the ...
1
vote
2answers
49 views

amplification of magnetic field

can we by any means amplify magnetic signal as we can with electric signal. As both electric and magnetic field can be represented in the form of a wave the analogy seems to be natural. I want the ...
9
votes
4answers
138 views

Is magnetic levitation a good way to vibrationally isolate a speaker from its support?

I recently heard about this company planning to sell a magnetically levitating bluetooth speaker. I understand that the levitation is partly motivated by visual aesthetics, but on the website the ...
1
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0answers
18 views

Very short physics question (electromagnetic field): Just draw the figure of the problem? [closed]

Can you please draw me the figure of the problem? I dont want the solution,just the figure? A straight, stiff, horizontal wire of length 25 cm and mass 50 g is connected to a source of emf by light, ...