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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26 views

May have solution to magnetic perpetual motion [duplicate]

The theory behind my design is if you can rotate the magnets as they pass a stationary magnet you can generate perpetual motion using magnatism as the only energy source. the design: if you ...
1
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0answers
39 views

Can a circuit produce a magnetic force on itself?

Well I think that it is kind of obvious, because the magnetic force does not specify if the fiel is produced or not by the circuit that feels it, but I had never heard about "autoinduced forces" or ...
0
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0answers
26 views

Clear, coherent electromagnetism textbook [duplicate]

I have recently finished a year-long introductory undergraduate course on electromagnetism, but I did not get a very good sense of how everything fits together conceptually. Are there any good ...
0
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1answer
25 views

How exactly does Magnetic Hysteresis lead to Power Loss in Transformers?

In reference to the Power losses in a Transformer, the author of Physics Textbook writes: As a result of magnetic hysteresis, the magnetic energy stored in the magnetic field as the magnitude of ...
4
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0answers
41 views

Why is there a minus in the Gauge Field Lagrangian kinetic term? [duplicate]

For vector Gauge fields we usually write the kinetic term: $$ \mathcal{L} ~=~ - \frac{1}{4} F_{\mu \nu} F^{\mu \nu}$$ while for matter fields e.g. for a real scalar: $$ \mathcal{L} ~=~ \frac{1}{2} ...
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29 views

Half wave antenna

I need to calculate the magnetic field intensity at a distance $x$ and angle $\theta$ for a half wave dipole antenna. I know the length of the antenna is $$ l = 333.33mm$$ and the magnetic field ...
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1answer
25 views

About field lines and continuity of magnetic and electric fields

In my laboratory class we were doing an experiment with grass seeds and iron filings to visualize the electric and magnetic field lines. So, we were discussing why they appear, because we know that ...
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0answers
54 views

can you explain the Lenz's Law **with** conservation of energy?

can you explain the Lenz's Law with conservation of energy?? there is another question in this website which explains it without conservation of energy but my emphasis is on explaining it, with ...
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0answers
36 views

Calculating instantaneous field strength for known signal source

I was referred here from electronics stackexchange. Suppose I have a time varying signal source V = Vm cos(wt). This source is fed to a half wave dipole antenna which in turn radiates electromagnetic ...
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0answers
40 views

Magnetic field of multiple loop turns?

Given this equation to calculate the magnitude of the magnetic field: $B = \mu_0 \frac{N }{l} I .$ Where $\frac{N }{l}$ is the number of turns per unit length. $I$ is the current, $\mu_0$ ...
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0answers
24 views

Conservation of Energy in induction due to variable current

An infinite wire with current is kept next to a square loop. Now, I change the current at a constant rate in the long wire. This would induce a current in the loop, the direction being determined by ...
3
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0answers
15 views

When do we have a coherent magnetization rotation? (single-domain particles)

So I am studying micromagnetics + spintronics and I am little bit confused with certain concepts regarding the physics of magnetic domains (especially single domain particles): What I already knew: ...
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25 views

Value of $E_x$ through an $X-\textrm{boost}$

Suppose I'm standing at the (0,0,0) point of a coordinate system and I see an electric field where $E_x=f(t,x,y,z)=\sin(x\cdot y\cdot z\cdot t)$ and at time $t_0=0$ I start moving on the x-axis at ...
0
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0answers
18 views

can we actually substitute electrodes in linac to electromagnetic coil?

I did some readings and researches for linear particle accelerator as I want to create one for my school science project. But I realised that most linac uses electrically isolated cylindrical ...
1
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0answers
42 views

Electromagnetic Tensor under Lorentz transformation, $F'(\Lambda x)= \Lambda F(x) \Lambda^T$?)

Suppose we have a configuration of electric and magnetic fields $E(x1,x2,x3,x4)$ and $B(x1,x2,x3,x4)$, they depend of position and time for a fixed coordinate system. And I want to know how someone in ...
0
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0answers
17 views

Hertzian Dipole Antenna

Hey guys have a physics question. I'm trying to find the current that is necessary to radiate a total power of $$60mW$$ Current is constant over dl and the length is equal to $$l=0.02*\lambda$$ I'm ...
2
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1answer
30 views

Shape of Eddy Currents

I've always had this question and didn't know how to answer it - Why do eddy currents have the shape they do? Why are they circular eddies?
3
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2answers
66 views

What is the purpose of the Maxwell Stress Tensor?

In the calculation of the forces acting on a charge/current distribution, one arrives at the Maxwell stress tensor: $$\sigma_{ij}=\epsilon_0 E_iE_j + \frac{1}{\mu_0} B_iB_j ...
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0answers
20 views

Conductor at the same potential

I'm trying to understand better the physic value that a conductor has in a static eletric field. We know that his potential is costant in and on it surface. But same potential should mean, if the ...
0
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2answers
35 views

What actually goes on in RLC circuit?

I already have difficulty understanding how each of the RLC circuit elements work individually as it is, and I have no idea how they work simultaneously in an RLC circuit. My schoolbook represents the ...
0
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0answers
13 views

Is the back induced emf in inductive coil equal to the original? [duplicate]

I always thought that an inductor resists the change of magnetic flux to a CERTAIN EXTENT, that is it would generate a back emf that would provide only a percentage of obstruction to the original emf. ...
0
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0answers
38 views

Magnetization of the source due to a stronger induced magnetic field?

Considering this classical diagram: From the top view, we can see a current carrying wire( flow of current is into the page) while an exterior magnetic field($B$) is applied perpendicular to it, ...
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0answers
28 views

Calculating magnetic field strength in gap of tapered toroidal electromagnet

Consider a toroidal electromagnet filled with a magnetic material of large permeability $\mu$. The torus contains a small vacuum gap of length $h$. Over most of its length the torus has a circular ...
0
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3answers
56 views

Electric Field Inside a Conductor at Different Charge Densities [closed]

We say that the magnitude of the electric field inside a conductor is zero, whether a hollow or solid. However, at certain charge densities, the magnitude of the electric field inside the conductor ...
1
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3answers
135 views

How to find the parts across which emf is induced?

Is there a general rule that will allow one to find the parts where the emf is induced? Consider for example the following two cases: Case 1: A rod is made to move normally to the magnetic field at ...
1
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1answer
25 views

Doubt about Motional Emf

In the derivation of a motional emf, we assume that as the conducting rod moves, the free electrons also move in the same direction as the conducting rod. However, the Tolman-Stewart Experiment showed ...
0
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1answer
22 views

Gauge transformation of wave function of a system of stationary charges

Let's say we have a system of $n$ stationary charges interacting via Coulomb potential. Let's ignore possible external electromagnetic fields. Moreover the system is quantum, and its wave function is ...
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1answer
42 views

What causes polarization current density in plasma?

Plasma current density is defined as $\textbf{j}=-\mathrm{e}n_e\textbf{u}_e$ where $\mathrm{e}$ is electron charge, $n_e$ is electron concentration and $\textbf{u}_e$ is electron velocity. What ...
3
votes
1answer
20 views

Suitable boundary conditions magnetic field paradox

Consider a point charge $q$ situated at the origin, and a uniform magnetic field, covering all of space, pointing in the $z$ direction $\mathbf{B}=B_0\hat{\mathbf{k}}$. What happens when you turn ...
2
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1answer
70 views

What exactly happens when total internal reflection takes place at a quantum level?

What happens when light interacts with the boundary between 2 mediums at a quantum level? Why is it totally reflected back when it is travelling from an optically denser to a less dense medium? How ...
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1answer
30 views

Is light an example of perpetual motion? [closed]

If a photon doesn't meet an obstacle it keeps going, can we talk about of perpetual motion?
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2answers
76 views

It's not the size of your magnet?

Growing up I've seen magnets on the fridge to the cows stomach and the latest that I know of, neodymium. On a molecular level what makes some magnetic material stronger and last longer than others?
5
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2answers
960 views

Does rest exist?

I initially thought that the concept of rest depended on an inertial frame of reference. So for example, if the Earth and everything on it were the only things in the universe, and the Earth was ...
5
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2answers
400 views

How does an electron move through a metal or a semiconductor

I understand that atoms in a metal or semiconductor are bonded and that they will have several eigenstates where electrons can reside. When a voltage is applied electrons in eigenstates will move to ...
0
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1answer
34 views

Vacuum permittivity and vacuum polarization

Is vacuum permittivity an effect of vacuum polarization, or are these unrelated phenomena? A more detailed way to ask this might be, is the vacuum analagous to a dielectric in that electron-positron ...
3
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0answers
10 views

orientation of heterodyne products

Let us take two man-made propagating polarized coherent RF waves at frequencies F1 and F2 of equal amplitude and direction. Assuming vertical polarization is assigned as 0 degrees, let F1 be at 0 ...
0
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1answer
48 views

Point source behind a diffusing plate? [closed]

I am confused about the action of a diffusion plate in optics experiments (e.g. with the Michelson interferometer). Let us say we put a point source behind a diffusion plate, what will the set up ...
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0answers
17 views

Energy density inside anisotropic materials

I'm taking some college courses on electromagnetism and there was some talk of energy stored by electromagnetic field and its density. The expression that we use to calculate energy density stored by ...
4
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1answer
75 views

Ultraviolet catastrophe in a classical world

In the real world, the ultraviolet catastrophe doesn't happen because the quantization of photons modifies the classical behavior of light at frequencies comparable to and higher than the temperature. ...
1
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1answer
28 views

Wave generated with particle excitement

To my understanding, an electromagnetic wave(infact two perpendicular fields) will be emitted when a particle(e-) shifts from higher energy orbital to lower energy orbital but what would be the ...
2
votes
1answer
66 views

Why do different vector potentials in Landau levels problem lead to different quantum mechanical ground state wavefunctions?

Consider a charged particle (electron) moves in xy plane under a magnetic field pointing along the z direction, i.e., $\vec{B}=B\hat{z}$. As a consequence, we can write down three different gauges- ...
0
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1answer
46 views

Help with relativistic notation (Derivative of Lagrangian)

I am trying to learn QFT, but I haven't taken a course in general relativity so the relativistic notation stuff is taking me a bit to get used to. I do not understand how to do the following. For a ...
0
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0answers
50 views

How can a coil work?

In a coil where all the wires are touching, why doesn't the current just go right from plus to minus? It seems like a huge detour for the current to pass throug the whole wire instead of just going ...
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0answers
21 views

Electro magnet strength to weight ratio

I was wondering. How would I work out how strong a magnet would have to be to support my weight.
0
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1answer
63 views

Is it possible to strip the magnetic, or electric field from a photon?

A photon is made up of a magnetic part and an electric part, but we can see the existence of these fields without the other one so I would like to know if it is possible to somehow separate one field ...
1
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1answer
48 views

Questions about Biot-Savart law and Ampere's law

A textbook I'm studying with described finding vector magnetic potential $\vec{\text{A}}$ from Biot-Savart law as below. ...
2
votes
1answer
30 views

Amplitude of voltage from centre tap rectifier?

Should be the amplitude of voltage obtained from a centre tap transformer be about half if not rectified? Because in centre tap the potential difference for each half cycle is taken a cross only half ...
1
vote
1answer
34 views

Quantum Mechanism Dipole Moment Magnetic Field Problem [closed]

I figured 1a out pretty easily. For 1b I am a bit stuck. So far i have that in the field: $$ \Delta z = v_0t + (1/2) a_zt $$ $$ F_z = ma_z $$ so $$ a_z = F_z/m $$ We know $$ ...
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1answer
64 views

What is the difference between the Lorentz force and the ponderomotive force? [closed]

I understand that Lorentz force is due to motion of moving charged particle in a magnetic field, and I imagine that ponderomotive force is mechanical version analogy to a person surfing on a wave ...
1
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0answers
37 views

Wind turbine design question [closed]

I am planning to design a wind turbine that is has rotor blade radius of 0.915m and is connected to a generator. The generators specifications are, it is an ac generator with 5000 coil turnings and a ...