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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Possiblity of predicting behavior of system when properties described as functions over space?

Suppose I am given a system that consists of a distribution of charged particles(which are all over space and are point-charges). They are described by a set of functions instead of variables. These ...
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1answer
38 views

Can someone please explain impedance matching and wave reflection?

I'm reading Wikipedia's article on impedance matching (http://en.wikipedia.org/wiki/Reflections_of_signals_on_conducting_lines) and this just seems so foreign to me. 1) What does it mean for a ...
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1answer
68 views

Differentiating the Hamiltonian Operator, $\hat{H}$

Firstly let $\hat{H}$ denote the full energy of the electromagnetic wave. I'm trying to differentiate the Hamiltonian operator with respect to the components of momentum, i.e. $$\frac{d}{dp_x} ...
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1answer
18 views

Permeability and magnetization of soft iron at various fields

I'm curious as to the magnetic permeability of soft iron (and other materials if available) under different fields. I know permeability of materials changes with field (that is why we have saturation ...
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0answers
23 views

diamagnetism in constant magnetic field

"The diamagnetic materials repel the materials which produces magnetic field, so putting these materials in the proximity of the magnetic field generating materials produces the effect of the ...
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0answers
24 views

Heavyside Lorentz units and Gaussian units

What is the relation between Heavyside Lorentz units and Gaussian units? From this Wikipedia article, I noticed there are $4\pi$ difference between them, but my TA wants more. Is there other ...
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1answer
16 views

Finding the direction of several radio beacons using a faraday cage and a radio receiver

I'm trying to build a system that can detect the direction of a set of radio beacons operating on the same frequency. In order to do this I have planned to use a normal radio antenna placed inside a ...
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2answers
214 views

Has magnetism been experimentally demonstrated at the quantum level?

I've learned that magnetic fields are generated by electric currents, and that electric current is the motion of electrons and stuff like that. Many textbooks also talk about "point charges" and have ...
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21 views

Quantized modes of EM field in a cubic cavity

I am trying to solve for Electric field modes in a cubic cavity with perfectly reflecting walls. I know that for the modes, I have the standard Helmholtz Equation $$(\nabla^2+k^2)E_i=0$$ And I want ...
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46 views

How to calculate the Induced Voltage Given Spinning Conducting Loop? Intro to Electromagnetics problem [closed]

I'm having trouble figuring out a different variation of this problem. On my homework, I'm asked to find the induce emf for the following B field: $$\vec{B}=50\vec{a_y}$$ I was able to figure out the ...
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1answer
28 views

What is the easiest way to demonstrate low magnetic flux NMR on the bench?

I'm trying to build my own low fux density bench NMR set-up, and am well-versed in electronics. Continuous Wave is supposed to be the easiest. I see commercial instruments that stimulate elements in ...
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1answer
89 views

Electromagnet force equation clarification

So, from a previous previous question, I know what plane the force from an electromagnet will affect a ferromagnetic material in. I thought that would be enough, but working through some problems ...
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2answers
60 views

Relationship between surface density and volume density

Often in an E&M problem, I'm having to "chop" an extended object into an infinite sum of smaller extended objects which I know more about to find a potential or electric field or whatever. The ...
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1answer
42 views

How to calculate current flowing down a wire connecting charge to ground

If charge Q is connected to ground through a wire, how would you calculate the current that flows as a function of time? No other information is given. I have not seen this type of problem in the ...
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0answers
25 views

Frequency dependence of refractive index $ n $ considering electron oscillator using Electromagnetic Theory

First and foremost, I am referring to Hecht, Zajac E. Optics 4th edition. I am reading the dependence of refractive index on frequency, and it goes well until Hecht jumped on his equation. First we ...
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0answers
20 views

Deriving Ampère's Circuital Law from Ampère's Force Law?

Ampère's force $d^2\vec{F_{21}}$ of current element $i_2d\vec{\ell_2}$ on $i_1d\vec{\ell_1}$ is$$d^2\vec{F_{21}}=-\frac{\mu_0}{4\pi}i_1i_2\frac{\hat{r}}{r^2}\left[2(d\vec{\ell_1}\cdot ...
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0answers
44 views

Does a conducting wire give off measurable radiation?

In the Drude model (semiclassical, but should still apply here I think), the conducting electrons are in a constant electric field, and, in between collisions with the lattice ions (that happen, on ...
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3answers
54 views

Transformers and DC voltage

Ok, if I have a transformer with 100 coils of the primary and 200 coils on the secondary and I connect a 9 volt battery to the primary, how many volts should I expect from the secondary coil? I know ...
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2answers
510 views

Is there a relationship between the energy of a photon and the energy of an electromagnetic wave?

If the energy of a photon $E_{p}=hv$ And the energy of an electromagnetic wave is $E_{w}\propto \hat{\mathbf B}^2$ What is the relationship between $E_{w}$ and $E_{p}$?
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1answer
48 views

Would a simple electric generator based on magnetic induction( magnet moving near coils to produce current) work in vacuum?

Would a simple electric generator based on magnetic induction( magnet moving near coils to produce current) work in vacuum? I mean if that generator would be connected to battery to charge it - moving ...
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1answer
27 views

Estimating the rotational speed of DC motor

What is the best strategy to roughly estimate the RPM of a simple DC motor as seen in this video?. I want to estimate the max possible rotation of the coil that has $n$ number of turns and has moment ...
2
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1answer
183 views

A James Clerk Maxwell Disproof

One of my favorite physicists to learn about was James Clerk Maxwell, for the fact that he unified the study of E&M in physics and he would often disprove theories that did not work as a ...
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2answers
37 views

Net Electrostatic Field inside a Conductor is $\vec{0}$

I've heard an explanation for this, and my professor wasn't really able to clarify my questions, so I was hoping someone could help: Suppose there is an electrostatic field $\vec{E_{net}}\ne\vec{0}$, ...
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1answer
31 views

Conditions for characterizing a wave as plane wave

Given a wave equation, say for example $\Psi(x,y,z,t) = a \cos\left(\omega t -\vec{k}\cdot \vec{r} \right)$, what conditions should be met for $\Psi$ to represent a plane wave?
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3answers
73 views

What is the relationship between $V(t)$ and $V(x,y,z)$

I was recently asked this by a friend. He told me that coming from a physics background, he does not understand $V(t)$ and he believes it is purely theoretical construct made up by circuit ...
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1answer
32 views

How similar is comparison between the principle behind Newton's Cradle versus AC Current moving down a transmission line?

Anyone who has taken high school physics has seen the following assembly. You drop one ball from the left hand side and the ball from the farthest right hand side gets knocked away. This is to ...
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3answers
173 views

Why can't electrons fall into the nucleus?

I read a book on pop sci book on quantum mechanics and the author said that electrons do not fall into the nucleus due to quantum mechanics- which principles suggest this (I think it was Heisenberg's ...
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1answer
48 views

Electric charge of light? [duplicate]

Light (or any radiation as a matter of fact) is an electromagnetic wave so why doesn't it have a electric charge associated with it? As far as I know only static or flowing electric chargers can ...
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2answers
86 views

Non-stationary capacitor

A common exercise in non-stationary electromagnetism is to find the electric and the magnetic field generated by a capacitor with round plates, if the potential difference between the plates varies in ...
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2answers
90 views

Physical meaning of imaginary part of Electric field?

As far as I know (or I thought I knew), if we have an electric field $$\mathbf{E}=\mathbf{E_0}\cos(\omega t - kx),$$ we can define it as the real part of $$\mathbf{E}=Re(\mathbf{E_0}e^{i(\omega t - ...
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1answer
264 views

Has NASA confirmed that Roger Shawyer's EmDrive thruster works? [duplicate]

This article states: But somehow, despite all of the reasons it shouldn’t work, it does. Scientists at NASA just confirmed it. Now in this question - it is strongly suggested that this ...
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0answers
36 views

Remote EEG Detection / Reading

I recently noted that Phillips, Accenture, and Emotive grouped together to create a proof of concept that would assist ALS patients to gain greater control of their lives through brain, voice, and eye ...
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2answers
178 views

What happens to a photon after it is absorbed by an antenna?

I recently have read about interception of wireless information, however this mentions that people can intercept the information, and then somehow the recipient also gets the information. Regardless ...
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1answer
60 views

Is it necessary for EM fields to be dependent & co-exist in static conditions?

I was having a discussion today with one my colleagues in the lab about the independence and co-existence of EM fields.$$$$ My argument: In time-varying fields: EM fields are necessary dependent, ...
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1answer
66 views

Is charge density zero in a dielectric material and why?

I'm trying to solve a problem involving parallel capacitor. I can't decide whether to use poisson's formula or laplace's formula. The question is, is there $\rho_v$ in a piece of dielectric and ...
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2answers
486 views

Frequency modulation using visible light

Currently I am doing research into visible light communication from an Embedded Systems background (MSc), but I am struggling to relate the concepts of modulation of radio to visible light. I already ...
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0answers
6 views

What is the difference between Linear and Non-Linear Magneto-optical effects?

Principle difference between Linear and Non-Linear Magneto-optical effects and how they affect the property of light passing through a Vapor medium.
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2answers
41 views

Does induced current affect the permeability of a material?

For electromagnetic wave propagation, we can typically characterize a medium by conductivity $\sigma$, permeability $\mu$, and permittivity $\epsilon$. Consider if this material had current passing ...
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1answer
29 views

Distribution of energy in an electric and magnetic field

Are the energy of the electric field and the energy of the magnetic field concentrated on their sources OR are they scattered in the environment where the fields arent zero? What is the formula that ...
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2answers
35 views

Question about electromagnetic Spectrum [closed]

I have question related to electromagnetic Spectrum. If energy of photon is $E=m_e c^2$, to which part of the electromagnetic spectrum does it belong ?
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0answers
19 views

Modeling magnetic field shielding

I am wondering what is the best way to model magnetic and electric field shielding from a magnetic dipole in the near field? For example, let's say you have a coil of current carrying wire in the x-y ...
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1answer
79 views

If you spin a magnet in space, far from any magnet field, would it spin forever, being able to produce electricity forever?

This is of course a purely theoretical question and it would take energy to get the magnet moving in the first place but once it's moving in the vacuum of space, with no gravity or magnetic field ...
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2answers
49 views

protons and electrons

I am a novice in physics and a few things are not clear to me in electromagnetism: Consider the experiment of giving a piece of metal positive charge (which I assume consists of protons), by keeping ...
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4answers
106 views

Why uncharged particles do not feel the Lorentz force? [closed]

Why uncharged particles do not feel the Lorentz force? Please do not answer with the formula $ \vec F = q\left( \vec E + \vec v \times \vec B \right) $. Edit after an answer which is an circular ...
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1answer
53 views

Dimensional Analysis in Electromagnetism (SI vs Gaussian-cgs)

Looking at Konopinski's formula for conjugate momentum (in the comment after equation 3 of "What the Vector Potential Describes"): p = M v + q A /c it is plain enough that M v is momentum, but if we ...
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1answer
75 views

Why three families of multipole moments?

There are three families of multipole moments: The electric multipole moments, the magnetic multipole moments and the toroidal multipole moments. Is there any reason why there are this three families ...
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3answers
370 views

Why does Snell's law not factor in wavelength?

If dispersion is caused due to different wavelengths bending with different angles, how is Snell's law right in generalizing it as $\sin(i) / \sin(r)$? Or am I missing something?
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1answer
35 views

Is the electron magnetic moment responsible for the Lorentz force?

My question about the sum of the electrons' magnetic moments in a wire(What is the sum of the electrons' magnetic moments in a wire?) had an answer which disappeared later. The answer was - if I ...
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2answers
37 views

Why can I blow up other potentials at the origin but not the one inside a dielectric sphere in an electric field?

While solving the electrostatic field for a dielectric in an electric field, we take the potential at origin to not blow and thus, we eliminate the inverse powers of r in the expression for general ...
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1answer
78 views

Finding the magnetic vector potential by calculus of variations

Given the functional $$F[A]=\int_{\mathbb{R}^3}\{\frac{1}{2\mu(x)}|\nabla\times\vec{A}|^2-\vec{J}\cdot\vec{A}\}d^3x$$ with $\vec{A}$ is a candidate vector potential for the field ...