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.

learn more… | top users | synonyms (5)

0
votes
1answer
67 views

Does alternating current come from DC?

I wonder whether alternating current is produced from DC current or whether AC and DC are entirely different concepts. Is there any relationship between AC and DC?
0
votes
3answers
192 views

Why in a solenoid, do the magnetic field lines resemble that of a bar magnet?

Each loop in the solenoid will have its own magnetic field wrapped around it. In that case it won't resemble the magnetic lines formed by a bar magnet...; but we see that it is the same. Why is that?
0
votes
2answers
92 views

why do magnetic field lines leave the north pole and enter the south pole? [duplicate]

suppose we have a bar magnet |S_______________N| ... we can imagine it to be |S-N-S-N-S-N-S-N| So, why do we see the lines leave the north pole and enter the south pole externally? What ...
0
votes
1answer
46 views

constant $c$ in Lorentz force

I met some of examples of force in studying classical dynamics, and Lorentz force was represented as $$ \mathbf{F}=\frac{q}{c} \mathbf{\dot{r}} \times \mathbf{B} $$ I've searched for meaning of $c$, ...
2
votes
2answers
108 views

Why does light fade from a room?

So basically in my toilet I have this really bright ceiling light, but when I turn it off it doesn't just instantly plunge me into darkness, but rather sort of fades out over a few seconds. It looks ...
0
votes
0answers
40 views

Electrolysis of Paramagnetic Ferric Chloride in Water

I'm trying to settle a bit of a debate between a friend and myself over the cause of an effect observed when dissolving Ferric Chloride, Iron(III) Chloride (FeCl3), in water and supplying an ...
0
votes
1answer
34 views

Alternating Current/Electromototive Force equaling 0?

All alternating current diagrams are drawn as sinusoidal waves that intercept with x axis. Given our usual sine wave that equals to 0 at 180° it would mean the alternating current would equal to 0. If ...
0
votes
1answer
52 views

Deriving electric field

Can anyone explain where the following expression for the electric field vector comes from? $$ \mathbf E(\mathbf r,t) = -\nabla \phi(\mathbf r,t) - \frac{\partial}{\partial t}\mathbf A(\mathbf r,t) ...
1
vote
1answer
25 views

a charged particle path [closed]

A particle of mass $m$ and charge $e$ enters a homogeneous and stationary electric field $E$ with velocity $v_0$ perpendicular to the direction of the field. Calculate the particle's path? What does ...
1
vote
1answer
19 views

Can iron be magnetized Via electric current in aqueous solution?

If you suspend iron particles in water and run an electric current through, the particles gather in a line along the current. Is this a form of magnetism?
4
votes
0answers
55 views

Building a Faraday cage for mobile networks that is transparent for optical wavelenghts

A friend of mine is working on an architectonic project, where she designs a Faraday cage type of open space built in parks or other public places. The initial thought is to build it from some sort of ...
0
votes
1answer
30 views

What are the advantages of Magnetocardiography?

I am reading the book Bioelectromagnetism by Malmivuo: Difference between the bioelectric and biomagnetic measurements lies in the sensitivity distributions of these methods. Diverse technical ...
1
vote
1answer
25 views

Is electricity constant in standard ECG device? [closed]

I am reading the book Bioelectromagnetism by Malmivuo et al. I am thinking if you need to use Maxwell equations in electromagnetism of ECG device. I am not sure if you need to change the current ...
1
vote
0answers
26 views

Conductivity Matrix (Symmetry Information)

I'm trying to understand the symmetry content of the conductivity matrix: one information is, presence of time-reversal symmetry causes the off-diagonal terms to vanish. When this is broken (e.g. in ...
1
vote
1answer
43 views

Direction of induced EMF(and current) and Lorentz force direction?

Is the right hand rule for the Lorentz force (given the current and magnetic field directions)and the direction of induced EMF the same?
1
vote
0answers
54 views

How to prove that the net magnetic force in an arbitrary current loop is zero [closed]

I believe that using Stokes' theorem makes this a laughing matter, because $$\mathbf{F}=\oint_C i d\mathbf{r} \times \mathbf{B}$$ Since the magnetic field is constant the $\nabla$ operator would ...
3
votes
1answer
56 views

Super Strong Magnets

I've seen the size of electric motors get smaller over the past 10-15 years...especially those used in small remote control vehicles like helicopters. I heard that the magnets being used in the ...
1
vote
1answer
50 views

Ampère's law and superconductors

I have been reading about superconductors and emerge me a inquietude about the explanation of existence of currents inside the superconductor while their magnetic field (inside too) is zero. Based in ...
2
votes
3answers
111 views

Self-energy of electron from classical reasoning

If it takes energy to group charge together(self energy) how can it be possible for every single electrons, etc, to have exactly same amount of charge? (think of if we hold some sand in our hand, then ...
7
votes
2answers
12k views

How does Hendo hoverboards achieve the self-propelling motion? What is the MFA?

From what I understand of the idea behind Hendo hoverboards, they use four disc shaped hover-engines to generate a self-propelling motion. I also understand that it uses Lenz's law and eddy currents. ...
0
votes
2answers
66 views

Is there a relationship between the diameter of a copper wire and the bandwidth it can carry?

I'd suspect intuitively that the bandwidth should decrease as the diameter decreases, but I don't have any reasoning to back it up. Secondly, would the actual wavelengths that it can carry, also ...
1
vote
0answers
75 views

The classical hydrogen atom

Suppose we want to analyze a hydrogen atom using purely classical mechanics. This obviously is not exactly how things work - quantum mechanics plays a huge role and probability distributions are ...
10
votes
6answers
837 views

Recommended books for undergraduate electrodynamics

What books are recommended for an advanced undergraduate course in electrodynamics?
1
vote
1answer
105 views

How can we derive the gauge field Lagrangian?

I learned the gauge field Lagrangian is given in this form: $$\mathcal{L} = -\frac{1}{4} \mathrm{Tr}(F_{\mu \nu}F^{\mu \nu}).$$ But how one can derive this equation starting from defining the ...
1
vote
1answer
45 views

Right Hand Rule for Proton Magnetic Field

I thought that right hand rule was for find the magnetic field generated by a current, where your thumb point in direction of the current. However, I was watching something that said we can curl our ...
1
vote
1answer
68 views

How to show that the force and velocity are perpendicular and that both have constant magnitude? [closed]

The force acting on a moving charged particle in a magnetic field $\hat{B}$ is $\hat{F}=q\left(\hat{v}\times \hat{B}\right)$ where $q$ is the electric charge of the particle, and $\hat{v}$ is its ...
0
votes
3answers
75 views

Energy Imparted by a Magnetic Field

As I understand it, when you switch on an electromagnet it generates a magnetic field that pervades all space, imparting potential/kinetic energy to every object with which it interacts. Where does ...
3
votes
1answer
64 views

Reflection of two electromagnetic waves

Can Electromagnetic waves be reflected by another electromagnetic wave without having any physical (transparent or opaque) material (i.e., in free space with one wave having twice the amplitude of the ...
0
votes
2answers
66 views

Why do we multiply the magnetic flux by the winding number?

A current I flows through a solenoid (with n turns). Self inductance is $L$. If the magnetic flux is $\phi$, I am taught that $-n\phi=LI$ I dont understand the part with $n$, why do we have multiply ...
0
votes
1answer
49 views

AC wire radiation

I'm trying to test my recently installed MEEP program for a very simple AC current. I know that for DC current, Ampere's law dictates that the magnetic fields must drop off as 1/r. How does this ...
0
votes
1answer
42 views

Really quick question about the order of operations in the Lorentz force

I'm trying to calculate the Lorentz force for a particle in a uniform electric Field, E and magnetic field B. The formulas is $$F=q(E+v\times B)$$ I'm just wondering what the order of operations is ...
0
votes
0answers
40 views

Magnetic field of magnetic screwdriver?

I wanted to know what is the typical strength of the magnetic field generated by the tip of a magnetic screwdriver, but couldn't find it anywhere on the manufacturers' webpages. So I was wondering, ...
8
votes
1answer
127 views

If protons and electrons had similar masses

If electrons and protons had the same mass, would they still be in a stable orbit around their barycenter, or would they eventually collide? Similarly, a positronium(or protonium) only lasts extremely ...
1
vote
1answer
93 views

How does EM radition depend on the reference frame?

In special relativity, magnetism is electrostatics in a different reference frame. This is how we explain the magnetic field being produced by moving charges (aka currents). Charges that move produce ...
0
votes
1answer
45 views

Direction of Induced Electric Field in a coaxial cable?

I was working through Griffith's book when I came across this problem: An alternating current, of the form $I(t) = I_0cos(\omega t) $ flows down a long straight wire, and returns (loops back) along a ...
0
votes
1answer
35 views

Potential energy given to an electron in a time-varying electric field

Given a general electric field $\epsilon(t) $ directed in the z direction, how would we calculate the potential energy given to an electron as a result of this field?
0
votes
0answers
33 views

Fusion plasma compression with liquid metal

General Fusion plans to use an imploding shockwave of molten lead to compress a magnetized plasma "spheromak" target in order to make it burn more efficiently. How come the lead does not quench the ...
0
votes
1answer
30 views

What are poles of a circular loop carrying current?

Why are the poles located where they are? How is an electromagnet formed? How can I determine the poles of an electromagnet? I'm confused about the polarity of a circular loop carrying current.
0
votes
1answer
37 views

The magnetic fields produced around a conductor carrying current are circular shaped [closed]

So what are the north poles and south poles of this conductor?...The magnetic lines are not entering or leaving from anywhere?
1
vote
3answers
42 views

Is a flow of ionized water an electric current?

If $H_2O$ ions have a net electric charge and electric current is the flow of electric charge, can a stream of water ions be considered an electric current? If so, is it conceivably possible (not ...
1
vote
1answer
51 views

Magnetic field of a static disk magnet

I have a magnetic disk (Radius R, height h) that creates magnetic field lines (axisymmetrical). I simulated the field lines, exported the data and am now trying to fit a function into the data to have ...
0
votes
0answers
50 views

Lorentz transformations an EM fields

When deriving the Lorentz transformation equations in undergraduate physics classes, teachers typically analyze the behavior of an ideal clock and a rigid bar. Once the behavior of clocks and rods is ...
0
votes
0answers
11 views

Aluminum magnetic moment in ZnO

I have made a density functional theory on calculation zno 2x2x2 super cell and I have substituted one of the Zn atoms with Aluminum and did spin polarized calculation. I expected that the unpaired ...
0
votes
2answers
46 views

Magnet arcs assemly

Is it possible to join multiple Neodymium magnet arcs (shown blow), which are radially magnetized, to create a cylindrical ring unity that is also radially magnetized? If it is not possible, how to ...
0
votes
0answers
12 views

Near field and Nuclear magnetic resonance (NMR)

Why does Nuclear Magnetic Resonance (NMR) physics not concern itself with near field physics? All resonance wavelengths in NMR are much larger than bough sample, pick-up coil and excitation coil. ...
0
votes
1answer
71 views

Relationship between polarization density and electric field

Imagine I have an electric field $E$ created due to some free charges. Then I introduce a dielectric material somewhere. What confuses me is the polarization field $P$, which is now proportional to ...
1
vote
5answers
226 views

What is divergence?

What is divergence? I was learning about Maxwells equations and don't understand the divergence part of it. Can someone give an intuition of what divergence is in relation to maxwells equation. To ...
1
vote
0answers
31 views

What is DX technology and what are the effects on digital cameras?

I am photographing in a high power voltage field in Industry producing aluminium, called DX technology. How do I know if my digital camera will not be affected? At 350kA current my film cameras were ...
1
vote
0answers
17 views

Two conductor's in a magnetic field, canceling each other's EMF?

If two conductor's are in a $\Delta$B, oriented the same in the field, and they induce equal $\epsilon$, can their wiring be oriented in a way that they can cancel each other's induced $\epsilon$? So ...
2
votes
1answer
103 views

Is the Wikipedia article on the Kramers-Kronig relations correct?

Reading the "Physical interpretation and alternate form" section of the Wikipedia article on the Kramers-Kronig relations, it says: The imaginary part of a response function describes how a system ...