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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182 views

What is the area in Faraday's law if we have only a piece of metal moving in a magnetic field?

If a piece of metal of length $l$ is moving with a speed $v$ in a region where there is a uniform magnetic field $B$ perpendicular to it, there will be a potential difference across its terminals ...
1
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1answer
163 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 ...
0
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2answers
28 views

The source and sink phenomenological description of charge - how realistic is it?

I've heard over and over an electron described as a source of the electric field, but that is a misleading term. Source makes one thing of a tap, with a constant flow of something coming out of it. ...
0
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0answers
29 views

What happens if I pass electric current through conductor magnet? [closed]

Good days everybody. My question is as seen at the title. What happens if I pass electric current through conductive magnet? If there's no conductive magnets, can we guess what would happen if there ...
3
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1answer
202 views

Magnetic Levitation : Confusion with Lenz's Law

Considering the above diagram, I am failing to see why the aluminium ring floats upwards rather than oscillates. I understand Faraday's law, but I am struggling with Lenz's law - as there is an ...
14
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0answers
502 views

Do intergalactic magnetic fields imply an Open Universe?

According to a paper on the arXiv (now published in Phys Rev D), they do. How credible is this result? The abstract says: The detection of magnetic fields at high redshifts, and in empty ...
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0answers
5 views

Dipole moment and magnetic power of permanent magmets(circular or disc shaped)

Is any circular or disk shaped permanent magnet has its dipole magnetic moment and if answer is no,then why and how are the behaves as magnetic materials or say that they show magnetic power?
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2answers
82 views

Most fundamental quantity in magnetostatics and magnetodynamics [closed]

In both elctrostatics and electrodynamics, the electric charge is defined as the most fundamental quantity. What is the most fundamental quantity in case of magnetostatics and magnetodynamics ?
3
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3answers
287 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 ...
11
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3answers
121 views

Can a magnet damage a compass?

I've heard the claim before that a magnet can ruin a compass, and was about to repeat it to my son when I realized it sounds like complete nonsense. Googling turned up such unsubstantiated and ...
2
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3answers
125 views

General relativity without curvature?

Is there a reformulation of general relativity without curved space time, just with fields (like classical E&M)? Edit: removed the part about E&M with curvature (multiple posts).
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2answers
145 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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0answers
14 views

How to divert water flow by magnetic field or static electricity or electricity?

Is it possible to make a magnetic or electric plate that prevent hitting water to itself or at least divert it? Which force is most effective, magnetic field or static electricity or electricity?
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2answers
2k views

Why is bandwidth, range of frequencies, important when sending wave signals, such as in radio?

So in wired/wireless networking and radio, signals are sent in form of wave. Then the concept of bandwidth comes in, which is the difference between highest frequency and lowest frequency in a signal. ...
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votes
3answers
103 views

Can we say that gravity(indirectly) is responsible for motion of electrons around nucleus? [closed]

From Wikipedia But because general relativity dictates that the presence of electromagnetic fields (or energy/matter in general) induce curvature in spacetime From Wikipedia An ...
2
votes
1answer
121 views

Divergence Theorem, mathematical approach to Gauss's Law?

Let $D$ be a compact region in $\mathbb{R}^3$ with a smooth boundary $S$. Assume $0 \in \text{Int}(D)$. If an electric charge of magnitude $q$ is placed at $0$, the resulting force field is ...
1
vote
1answer
46 views

Using ion beam to create strong magnetic field

Consider, I want to make very strong magnetic field in some spot in space ( focus ) but I cannot put any solid material ( like metal conductor, or superconductor ) close to that spot (e.g. because ...
3
votes
1answer
156 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 ...
2
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2answers
104 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 ...
4
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2answers
210 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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0answers
31 views

Electromagnetic Waves and Magnets

Does an electromagnetic wave have an affect on a permanent magnet or on a piece of metal? When light hits a regular bar magnet is there a magnetic push or pull on it? And Does an electromagnetic ...
0
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2answers
41 views

Energy in conductors with $\vec{E}$-field

The question is deceptively simple. Suppose I have a uniform circular wire in which I have created the a E-field by some mean. We that without the source the electric field should not be there, so if ...
0
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0answers
118 views

Electrical Resistance of Spherical, Contacting Colloids

So, I work a lot with Magneto-Rheological (MR) fluids - which are essentially electrolyte solutions with suspended, paramagnetic colloids/particles. Once a magnetic field is applied to such a fluid, ...
2
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3answers
58 views

Observing a photon during flight

When I was reading about the double-slit experiment in quantum mechanics, everything seems to make sense in terms of the waves and the interference pattern, but if thinking more about this ...
0
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3answers
45 views

Rate of change of current in an Inductor

Considering an Inductor in a DC circuit: when the switch is first closed there is a change in current through the inductor, which induces an emf in the opposite direction (Lenz's Law). My question is ...
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0answers
5 views

What does magnetic flowmeters measure?

What parameter does the magnetic flowmeter actually measure? Velocity of the conducting liquid flowing through it or the amount of conducting liquid directly? The volume of liquid can be calculated ...
2
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2answers
302 views

What are the specific electronic properties that make an atom ferromagnetic versus simply paramagnetic?

As I understand it, paramagnetism is similar in its short-term effect to ferromagnetism (spins of the electrons line up with the magnetic field, etc.), though apparently the effect is weaker. What is ...
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0answers
19 views

What is direction of induced current in a rotating rod pivoted at one end in a magnetic field?

This is rod of length l, placed on metallic ring of the same radius as rod's length. This set up is placed in a magnetic field perpendicular to the rod and into the plane. It is very clear that an ...
10
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3answers
5k views

Can superconducting magnets fly (or repel the earth's core)?

If a superconducting magnet and appropriate power supply had just enough $I\cdot s$ (current $\cdot$ length) so that when it was perpendicular to the earth's magnetic field, the force of the ...
0
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2answers
40 views

An IE IRODOV Electrodynamics problem

A ring (radius R) is given a negative charge -q and at the centre a positive charge +q is kept. We have to calculate the electric field on the axis of the ring at a distance X from the centre. Take ...
2
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1answer
59 views

When to use separation of variables in E&M? [closed]

I'd really like to know if there is a fast way to recognize if separation of variables is the most appropriate way to go about solving a problem. Are there any kind of guidelines for when to use ...
1
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1answer
61 views

Does a charged particle propagating in free space have a 'self-energy' like term due to it’s interaction with the fluctuations of the quantum vacuum? [closed]

Does a charged particle propagating in free space have a 'self-energy' like term due to it’s interaction with the fluctuations of the quantum vacuum? (particle-antiparticle pairs popping into and out ...
-1
votes
1answer
89 views

Negative power measurement of transformer short-circuit test. What happened?

I have a dissectible transformer, made up of two 120-turn coils. I connect a function generator to the primary side, set the AC voltage to be constantly 10V, and short circuit the secondary side. And ...
0
votes
1answer
366 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 ...
0
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1answer
127 views

Can the physical properties of the EM field be described directly from the 4-gauge potential?

I'm trying to make an argument that classically, the EM field is considered a more 'real' physical quantity than the potentials, and am tempted to say that the fact that the field carries energy & ...
0
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2answers
110 views

Two different electrostatic charges in rotation

It's a theoretical problem. I mean I drawn a circle and I consider this circle exist. I would like to understand how works this device composed of a circle and two charges: Two charges fixed on a ...
0
votes
1answer
100 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 ...
1
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1answer
87 views

problem on electromagnetic induction and newtonian physics

Please imagine a solenoidal toroid (i.e. a donut shaped inductor) powered by an AC voltage source. It creates a changing magnetic field which is confined to the interior of the toroid (i.e. within the ...
2
votes
3answers
825 views

Curl of an electromagnetic wave

I can't understand the concept of the curl of an electromagnetic wave. $$ \nabla \times E = -\frac{\partial \textbf{B}}{\partial t} $$ All of the examples I find show a current through a conductor, ...
2
votes
2answers
49 views

Question regarding Van De Graff generator Belt

I have made a VDG generator with a rubber band as the belt and a glass roller. It doesnt seem to work because I think the rubber band may be conductive. I was thinking of using other materials for ...
4
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2answers
434 views

Why my simple electromagnetic experiment does not work?

I make a setup (see attached picture). ONE coil (1" diameter x ~120 turns), which is separated with a gap, is mount on two sides. Each side has an iron rod (1" diameter x 6" long) to increase the ...
1
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1answer
109 views

Predicting path of light?(general relativity and electromagnetism)

In the first image we can see bending of light by gravity,in the second image I placed a big glass(it almost has zero weight) of considerable thickness near sun which will refract light coming ...
0
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3answers
60 views

Rate of Acceleration of an Object Pulled by Magnetic Force

Gravity on earth pulls objects toward it with an acceleration of 9.8 m/s/s on Earth until the object reaches it's max potential free fall speed. (I call this terminal velocity though I think that this ...
2
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0answers
15 views

Which part of a real Type II Superconductor magnetization loop represents the Meissner state?

So if we consider an ideal type II superconductor the magnetization should look like this The Meissner state is to be found between $0$ and $H_{c1}$ and the superconductor works as an ideal ...
0
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1answer
71 views

Why we unified electromagnetic and weak force?

We have unified electromagnetic and weak force into one single force called Electroweak force. I mean we can use these different forces within their respective domains like weak interaction for short ...
2
votes
1answer
40 views

How large or small can frequency in the EM spectrum get?

The largest frequency range is gamma rays, but does the EM spectrum 'stop' somewhere? Like is there a limit to how large a frequency can get? Or how small frequency can get? Is it one of those things ...
3
votes
1answer
493 views

Homopolar motor and Lorentz force

My second grader thought making a homopolar motor for her science experiment would be fun. And, it was. Now I am trying to explain how it works and the Lorentz force. Please help me by giving me a ...
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0answers
22 views

Can I disperse a droplet with electromagnetic fields?

If I have a droplet of water, can I apply an electromagnetic field in order to disperse the droplet into smaller subdroplets (tiny vapor) and fill a space with them? The same way that magnetic dust ...
0
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0answers
21 views

How does permanent magnets attract each other if the $B$-field can do no work? [duplicate]

How can two permanent magnets do work on each other? If you put two magnets with opposite poles facing each other they will attract each other. If you put them with the same poles facing each other ...
1
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1answer
33 views

Is Magnetic field inside solenoid dependant on volume of its shape?

There are two types of solenoids: one cylindrical, one spherical. Let's assume the dimensions of the cylindrical solenoid are set such that its base radius is that of spherical solenoid $a$, and the ...