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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99 views

What is the physical meaning of Lorenz gauge condition? [closed]

What is the physical meaning of Lorenz gauge condition? And what part of the solutions we throw?
5
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1answer
129 views

A “figure-8” EM field created by a dipole antenna

This question pertains to the EM field of a Pulse W5017 dipole antenna. The data sheet of this antenna can be found here (which contains information regarding the radiation patterns). There are TWO ...
2
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1answer
71 views

Confusion regarding conductors and their behavior

Consider two thin plates and one thick plate(all conducting). A and C are the thin plates, B is the thick one. Now B is inserted between the parallel plates A and C. A is given a charge 2q and C is ...
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0answers
25 views

B field, reaction to magnetic medium

I've read 'if you put a magnetic medium into a conductor loop the B-field will change everywhere while if you put an electric charge into a dielectric sphere the dielectric sphere won't have any ...
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1answer
24 views

What would occur between the parallel plates of the capacitor?

In capacitors dielectric materials are sometimes inserted between the parallel plates. What would happen if a diamagnetic, or a paramagnetic material is inserted between the parallel plates of a ...
8
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4answers
278 views

A contradiction between Biot-Savart and Ampere-Maxwell Laws?

I came across a problem that I cannot get my head around. Consider two very small spherical metallic balls given charges +Q and -Q. Assume that they can be approximated as point charges. Now, they ...
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2answers
51 views

Does a displacement current have to be included in the Biot Savart Law?

Consider two spherical balls given charges of equal magnitude and opposite signs. Now, we connect them with a conducting straight finite wire. A current will flow in the wire till the charges on the ...
2
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0answers
77 views

Is radiation perpendicular in brehmsstrahlung?

wiki says: Bremsstrahlung is electromagnetic radiation produced by the deceleration of a charged particle when deflected by another charged particle, typically an electron by an atomic ...
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3answers
62 views

Electron deflected by moving magnet

My original question was far too long, so I am editing it down to this much smaller version: The Lorentz force for an electron traveling through a uniform magnetic field with no electric field is $F=...
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0answers
19 views

Does removing half of toroidal ferromagnetic core significantly reduce flux density in the remaining half?

Assuming a DC current in a cable has induced a magnetic field around the cable, and a ferromagnetic toroid is used to concentrate the field; if half of the toroid were cut away (so the cable is no ...
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4answers
2k views

To what extent can speed of light be reduced? [duplicate]

Light slows down upon entering different transparent objects, and the ratio is taken as refractive index of the object. If light can be slowed down, then is there a limit up to which it can be slowed ...
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1answer
38 views

Why can't weak core-less electromagnets be used in conjunction with strong permanent magnets to perpetually harvest energy?

Why can't weak core-less electromagnets be used in conjunction with strong permanent magnets to perpetually harvest energy? Magnets will attract ferrous materials but some materials like copper or ...
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0answers
20 views

Time derivative of total angular momentum in Dirac equation

I would like to calculate the time derivative of the total angular momentum of a Dirac particle in an electromagnetic field $(\vec A, \phi)$: $$\vec J = \vec r \times (\vec p - \frac{q}{c} \vec A) + \...
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0answers
12 views

Using a magnetometer in a sub-sea application, how to get a good magnetic bearing?

Mechanical engineer here, getting in over my head concerning magnetic sensors, electronics and the like :-) Quick situation description:For a work-application I am looking at using a MEMS based 3 ...
2
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2answers
63 views

Why would a moving infinite region of magnetic field exert an electric force?

I'm confused about the Lorentz force in relation to the frame of reference. There are many questions about that here, but I still don't get it. I've tried to break it down to the most basic example. ...
3
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1answer
25 views

Transmission line model proof?

Why 2 distributed lines is represented with series inductor and resistor along with parallel capacitor and resistor? What is the motivation for that? In circuit theory I Knew the assumptions to ...
1
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2answers
63 views

Could superconducting magnets be used to form a shield around a spacecraft?

If superconducting magnets could be used in space to form a field around a spacecraft of a similar field strength on the earth 25 to 65 microtesla's? Would the temperature in space at -246c be OK ...
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0answers
13 views

Will non-ferrous materials like Gold that have been magnetised by a slight electric current become attracted to much more powerful permanent magnets?

If a magnet interacts with Gold it will magnetise it to a very slight degree but if the gold is in turn magnetised by passing a generally weak current through it will the gold more easily attract ...
2
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1answer
21 views

Appears the world more reddish due to our vitreous body in our eyes?

Our vitreous body in our eye consist mostly of water. The refractive index of water is 1.33. If ligth is refracted the frequency stays the same but the wavelength will get shorter to equal to the ...
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1answer
69 views

Feynman path integral interpretation of the Aharonov Bohm effect [closed]

I have recently been reading about the interpretation of the Aharonov-Bohm effect via Feynman's path integral (see viXra:1403.0950). I do not know whether I am missing something, but I do not ...
3
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1answer
32 views

Why does a laserbeam bent downwards when shined through a solution of salt?

When you have a aquarium with salt on the bottom and add water to it the salt will solute in water, but most of it will initially probably stay more or less down. Now is you shine a laserbeam through ...
0
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0answers
41 views

How does a charged body sense the presence of another charged body? [duplicate]

If a charged body B is placed within the electric field of another charged body A,then B senses a repulsive or attractive force exerted by A. But how does this information actually transfer from A to ...
3
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1answer
42 views

Electron traveling through gravitational and magnetic field

When an electron travels through a magnetic field it experiences the Lorentz force. The force acting on the electron causes an acceleration and therefore Cyclotron radiation is emitted. After reading ...
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0answers
45 views

Can Lenz's rule really be used to determine the direction of induced current?

Faraday's Law states that the induced emf in a closed circuit is the negative of the rate of change of magnetic flux through the surface enclosed by the loop. To obtain the direction of the induced ...
4
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1answer
279 views

Why do planets not radiate EM waves in their orbits?

Despite being overall near-netural, I would expect the individual electrons and proton to radiate long EM waves as we accelerate around the Sun or rotate around our poles. Is the acceleration so small ...
4
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0answers
57 views

Why isn't cosmic microwave background radiation on Earth drowned out by thermal noise

The Penzias/Wilson experiment, which detected the CMB, doesn't sound feasible given thermal noise. When Penzias and Wilson reduced their data they found a low, steady, mysterious noise that ...
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0answers
84 views

Does the motion of a free electron in a plane wave electromagnetic field have analytical solutions?

Does the motion $[x(t), y(t), z(t)]$ of a free electron in plane wave electromagnetic field have analytical solution (oscillating E and B fields)? The Lorentz force is : \begin{align}m_e\begin{...
2
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2answers
38 views

How strong is Earth's magnetic field in space?

I've been searching around Google and Youtube about the strength of Earth's magnetic field. By the help of wikipedia, I have found out that it's magnitude is 25 to 65 microtesla or 0.25 to 0.65 Gauss ...
3
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0answers
65 views

Can the Hall effect drive a current?

In the Hall Effect current is passed through a wide strip of metal in a perpendicular magnetic field. Since (some of) the negative charges in the metal move but the positive ones stay put, the ...
1
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1answer
45 views

Good book to grasp physics [duplicate]

I'll try to be clear. I'd like to ask you if you know some books or chapters in textbooks which explaining the "meaning" of some physical phenomena or entities. I may try to be more specific using ...
1
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2answers
31 views

How to prevent magnetic field from generating in current carrying conductor?

Is there anyway to prevent generating magnet field or nullify it.
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0answers
47 views

Hamiltonian formulation of the semiclassical Model of electrons

I'm currently reading the book Solid State Physics by Neil W. Ashcroft and N. David Mermin. In Chapter 12 they introduce the "Semiclassical Model of Electron Dynamics". In short: After having solved ...
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0answers
35 views

Clarify example of Faraday's law

Im wondering if it is possible to induce a high voltage current (above 1k Volts), simply using a falling magnet and a copper wire - it probably is, but then what does it take to do so. I've done ...
0
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1answer
27 views

Can antennas work with high frequency EM waves?

Antennas usually work with FM waves, and AM waves, which mostly used in telecommunications. Information is transferred on FM, and AM waves by a transmitter transmitting information on these EM waves. ...
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1answer
13 views

How would I construct an EMI shield for low frequency EMI?

By low frequency, I mean 30-100 Hz. Would a Faraday cage or something like it be feasible? I am trying to shield two separate locations on a high voltage cable.
5
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1answer
22 views

Reason for poor signal strength of cellular phones inside a steel frame building

I could not clearly interpret the answer of the following question. So, hereby I wish someone could just make it easy to understand. And my question is: What makes the poor signal strength of cellular ...
3
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1answer
192 views

Hearing background noise from earphone while there isn't any connection

Once my friend told me that he was listening some background noise while his earphones were not plugged in any device. I didn't believe him but 10 minutes ago I experimented the same. I can certainly ...
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0answers
24 views

superposition of two magnets

If I have two magnetic particles at x and y axis with strengths* $\mu_{x}$ and $\mu_{y}$; and another magnetic particle in x-y plane with strength $\mu=\vec{\mu}_{x} + \vec{\mu}_{y}$,then will the ...
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1answer
86 views

Is the electric force a vector or a vector field?

The electric force (Coulomb's law) on a point charge $Q_2$ due to $Q_2$: \begin{gather*} \mathbf{F}_{12}=\frac{Q_1Q_2}{4\pi\epsilon_0}\frac{\mathbf{r}_2-\mathbf{r}_1}{|\mathbf{r}_2-\mathbf{r}_1|^3} \...
6
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1answer
135 views

What force causes the induced EMF of a loop? And, the difference between a loop EMF to motional EMF?

If a loop of wire is placed perpendicular to a changing magnetic field, there is an induced EMF such that the induced current is flowing in a direction to create an opposing magnetic field like this ...
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2answers
58 views

What does an oscillating magnetic field produce? [closed]

An alternating current produces a magnetic field. A oscillating charge produces light, which is an oscillating electric, and magnetic field mutually perpendicular to each other, and their motion is ...
1
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1answer
36 views

Photon as a gauge boson for static fields

Excuse me if my question is naive, but I have never taken a proper QFT. I used to think of a photon as a quantum of EM field, quantum of light. But form QFT and particle physics prospective, photon ...
1
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3answers
42 views

Is the South Pole of an electromagnet always at the end where current is drawn into it?

I'm trying to determine in which direction a magnetic field will be produced in regards to the direction of current in an electromagnet. Will the end of the electromagnet from which current is drawn ...
5
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0answers
57 views

Validity of gauge fixing in classical electrodynamics [duplicate]

I am working through Griffith, and was confused by some of the restrictions he imposed on the potentials in introducing the Coulomb and Lorenz gauge. It is easy to see that adding some arbitrary ...
1
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1answer
52 views

Could a man float in a large enough magnetic field to simulate zero gravity?

I know the magnetic field would need to be very large, but if an organisation like NASA with huge funding and resources could build a large enough device, could a man float in that magnetic field to ...
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1answer
28 views

Why does the magnetic field of the induced current oppose the change in the external magnetic field? [closed]

Why does the magnetic field of the induced current oppose the change in the external magnetic field? please help me to solve this Link:http://d2vlcm61l7u1fs.cloudfront.net/media%2F4dc%2F4dc03c3b-...
1
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0answers
29 views

How is there not an infinite regress in the emf of a motor?

Say we have a coil connected to a battery in a uniform magnetic field, perpendicular to the magnetic moment of the coil. This is a simple motor. There is a torque on the coil that varies with the ...
0
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1answer
45 views

How much and what kind of sunlight passes through a cloud?

I've read that 80% of sunlight is passing through clouds. Now there a small clouds and big clouds so it should be some average. Is this true or is the amount of sunlight passing throug a cloud really ...
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1answer
47 views

Find the electric field of a uniformly polarized sphere

The problem statement, all variables and given/known data We want to calculate the field of a uniformly polarized sphere of radius=R Relevant equations $$V(\vec{r}) = \frac{1}{4 \pi\epsilon_{0}} \...
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0answers
11 views

Determining pole strength experimentally

Could anyone give me a quick explanation of what magnetic pole strength is or a website that does so? Also, how can i determine this value experimentally? Thanks in advance