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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15 views

BOOST FM RECEPTION

How can i improve fm reception on my nokia smartphone? I have tried by removing the insulation on earphone wires and connecting the earphone wires to another wire placed high on roof but has not ...
0
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1answer
41 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 ...
8
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4answers
798 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. Can all voltages (potential differences) that exist in reality be ...
2
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1answer
29 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 ...
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2answers
31 views

amplification of magnetic field

can we by any means amplify magnetic field 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.
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4answers
61 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 ...
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0answers
17 views

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

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, ...
2
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6answers
88 views

Do electrons flow only on the surface of a wire?

Since the $\vec{E}$ field inside a "perfect" conductor is zero, do the electrons(the current) flow only on the outer surface? This has bothered me since I studied electromagnetism. Thank you for ...
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2answers
48 views

Current Density

I'm trying to understand the definition given on my electromagnetism course for the current density. More specifically, I want to know why, as defined below, the current density is given the name ...
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0answers
23 views

calculating electrostatic force [on hold]

I am trying to answer this question: Calculate the electrostatic force on a metal ion carrying a charge of $3.2$x$10^-$$^1$$^ 9\ \text{C}$, and which is in an ionic solution between two parallel ...
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0answers
17 views

Splitting of degenerate energy levels with a perturbed particle in a box

Suppose you have a particle in a square box $[0,L]\times[0,L]$. As the box is a square, the (2,1) and (1,2) eigenfunctions will have the same energy. If you were to apply an oscillating electric field ...
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0answers
29 views

Sequence of E and B field in radio waves and in single photons

In antenna technology we distinguish between nearfield and widefield. In the nearfield the electric and the magnetic fields are shifted by 90°. If you look closer you can see that there are two ...
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1answer
37 views

How much power you might need to generate dangerous EMP shock?

While playing with voltage multiplication and capacitors, I began to think if my experiments could damage my electrical equipment (eg. mobile phone) by creating strong magnetic fields over a short ...
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0answers
18 views

Physical reason for magnetic mirroring?

I understand the mathematical derivation of magnetic mirroring, which usually starts from the conservation of the magnetic dipole moment (e.g. in a plasma). But physically: a mirrored particle is ...
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0answers
21 views

Poynting Vector Volume Integral Inside a Cavity

Given an electromagnetic wave in resonance mode in a vacuum cavity inside a perfect conductor, on the boundary, the parallel component of $E$ field vanishes, and the perpendicular of component of $B$ ...
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0answers
25 views

Smallest view-able object by radio wave magnification with metamaterial?

What is the theoretical and in practice microscopic maximum/best resolution of a meta material radio wave lens (assuming diffraction or beyond diffraction techniques)? I'd like to use diffraction or ...
0
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1answer
48 views

Transformer ratios - 1:2 vs 50:100

I am only the equivalent of a high school student, so please, if possible, don't answer this question with anything too complex or really advanced university level. I am very happy to research new ...
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0answers
27 views

Circuit breaker Trips during thunderstorm

The circuit breaker at the electrical mains trips at home when there is a thunderstorm outside. Why does this occur?
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1answer
24 views

Magnetic force and relative frame

The magnetic field for to a moving charge depend on its velocity (Biot Savart's law). My question is that is it then not frame dependent? If it is, it means if a man is walking and other is standing ...
3
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3answers
55 views

Ampere's law and external currents

In Ampere's law the current outside the curve taken is not included in the expression. Does this mean that only the currents crossing the area bounded by the curve taken contribute to the magnetic ...
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1answer
21 views

Single Photon emission from positronium in strong magnetic fields; how is momentum conserved?

I recently came across a paper (which I will not describe in detail, however, the authors examine the probability of positronium producing a single photon, while under the influence of a strong ...
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2answers
70 views

Electromagnetic induction of an uniform magnetic field

EDIT: Thanks to the first answer, I may see that there is differences between a giant solenoid and a completely uniform magnetic field. Therefore it would be great if one can explain to me both the ...
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1answer
126 views

Total Momentum From a Standing Electromagnetic Wave

How does one show the momentum imparted to a perfect conducting resonance cavity (boundary) of any shape by a classical standing electromagnetic wave inside is zero? It should be by conservation of ...
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1answer
49 views

An electromagnetic induction problem [on hold]

The question goes like this : A thin non conducting horizontal disc of mass $m$ having total charge $q$ distributed uniformly over its surface, can rotate freely about its own axis. Initially ...
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0answers
25 views

Ampere's law question regarding magnetic field [on hold]

In amperes law the current outside the curve taken is not included in the expression u.i does this mean that the magnetic field calculated by using this law gives contribution of only the currents ...
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0answers
24 views

Broken bar magnet repels? [duplicate]

Why a bar magnet broken from between repel on joining again even if the poles are opposite, i.e. North and South.
3
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0answers
61 views

What is the derivation of the speed of light $c$ that is not based on electromagnetism? [duplicate]

The "speed of light" is not just the speed of electromagnetic radiation, but of any massless particle. Therefore must not there be an expression for $c$ that is not in terms of $\mu_0$ and ...
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1answer
37 views

Calculating the magnetic field due to a rotating ring using Biot–Savart law

I wish to calculate the magnetic field due to a charged ring rotating about an axis perpendicular to the plane of the ring and passing through a point on its circumference $(P)$. I arrive at something ...
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0answers
20 views

can I run a customised wind generator in reverse [closed]

I want to run a customised wind 12v Geni (no blades) in both directions will I get the same 12v in both directions.
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2answers
76 views

How does a fixed amount of transmitted radio energy supply an unknown number of destinations?

I did some maths and physics up to the age of 18, and hold an amateur radio licence. This thing has puzzled me for a while - does reception of an electromagnetic wave imply an interaction with the ...
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0answers
17 views

Weak localization and constructive interference

To my knowledge weak localization is a result of constructive interference between scattering processes and their time reversed. Traveling a given path in a vector potential leads to the phase $q\int ...
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0answers
34 views

Spin-dependence of the directionality of dipole radiation

I am interested in understanding how and whether the transformation properties of a (classical or quantum) field under rotations or boosts relate in a simple way to the directional dependence of the ...
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0answers
30 views

Explain the infinitude of magnetic flux about a finite length of wire

Ok so it is clear the flux caused by an inductor is limited. If I integrate about a flat spiral inductor I will find that the flux lines going up are a fixed quantity. Since every flux line going up ...
2
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0answers
41 views

About memory effect in E&M when E and B field has dependence in the history of E and B fields

How should one define the memory effect in E&M formally? What is the physical way to visualize the memory effect? How should one understand it intuitively?
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0answers
28 views

Why magnetic field generates around current carrying wire? [duplicate]

Why magnetic field generates around a wire when current flow through it ?
3
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1answer
116 views

EmDrive Cavity modes

The EMDrive described in patent application GB 2493361 is a simple section of a sphere surrounded by a superconducting cooling system. I have attempted to solve the oscillation modes possible and ...
2
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2answers
87 views

Doubt regarding Ampere's Circuital Law

The Ampere's Circuital law states $$\oint B\cdot d\ell~=~ \mu_0I$$ We can use it to derive the magnetic field of an infinitely long current carrying wire easily. My question is, why does the wire ...
3
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2answers
75 views

Utility of gauge four-potential $A_{\mu}$ (as opposed to electric and magnetic fields ${\bf E}$ and ${\bf B}$) in E&M?

The action for an electromagnetic field with source charges is given by $$S= \int \left\{ \frac{1}{4\mu_0}F^{\mu\nu}F_{\mu\nu} - J^\mu A_\mu \right\}dx$$ By setting $dS=0$ and taking the Lorenz ...
8
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2answers
124 views

Which of these theories on why light slows in media are true?

This question is similar to previously asked questions, but the responses to them are confusing and I think it may be better covered by listing out all the potential answers for clarity. It's a ...
0
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1answer
21 views

Self inductance & time constant formula

Is this a correct formula for calculating the induced EMF of a wire after the current stabilizes/ or while it stabilizes in the beginning of a DC circuit? What is the difference between the above ...
0
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1answer
11 views

Induced emf in stationary conductor lying in varying magnetic field

We explain that motional emf is induced because charges in a conductor move along with the conductor and as a result a magnetic force pushes them to one side of the conductor. But in case of a ...
3
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1answer
54 views

Optical absorption in multilayer structure

Assume a hypothetical 3 media/ 1 layer structure with the following indices of refraction: $$n_1 = 2, n_2 = 2+i0.5, n_3 = 1$$ where the thickness of the layer is 100 nm and wavelength = 1000 nm. ...
4
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2answers
130 views

What restores balance to a repulsive electric force on an electroscope?

I am an amateur physics enthusiast (during the day I am a police officer), and recently, I learned how to build an electroscope. I regret that I am learning how wonderful our universe is so late in my ...
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0answers
40 views

Penetration and skin depth in 'metallic' magnetic induction tomography (classical electromagnetism)

Does anyone know how AC magnetic fields behave in 'metallic' magnetic induction tomography (MIT). Do they form a magnetic circuit around a metallic specimen or penetrate through it, or both? This ...
0
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2answers
20 views

Effect of variable permittivity

If I immerse a rod vertically in a liquid with a relative permittivity gradient (the permittivity decreases with depth), will the rod stretch (will the spacing of the atoms in the rod be affected by ...
1
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0answers
16 views

Make an Electric motor work with help of 4 magnet wheels? [closed]

I am working on a car prototype that should work on the electricity that it generates with the help of magnets. The strong magnets will be fixed at the wheels. A Coil of thin copper wire(solenoid) ...
2
votes
1answer
47 views

Magnetic Field in the presence of a conductor

I am studying for my quals and came across an old question that reads like the following: There are two regions in space separated by an infinite conducting plane. Region 1 has a magnetic dipole ...
1
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1answer
46 views

Magnet substitution [closed]

I wonder if the two magnet configurations below are equivalent. If they are not - what will be the effects on the flux?
0
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0answers
53 views

Why did the Aharonov-Bohm effect mystify people? [duplicate]

Of course it is intriguing. But I think the Schroedinger equation for a charged particle in a magnetic field was known at the very beginning of wave mechanics. Therefore, the A-B effect should not be ...
1
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1answer
26 views

Magnetic multipoles in spherical harmonic

Does someone know explain me how to identify the multipoles magnetic terms of the multipolar expansion (Dipole, quadrupole, etc) in spherical harmonics?