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)

1
vote
1answer
40 views

How is magnetism ''conducted'' through a non-magnetic metal?

I have a ball of metal about an inch in diameter and a concave disc of another metal (which is magnetic) around the ring of the disc (about $12 {\rm mm}$ in diameter). I don't know which metals they ...
0
votes
1answer
40 views

Electromagnetic waves and group velocity

I have three questions about electromagnetic waves and was wondering whether anybody here could comment on these things: Wikipedia says that there are no longitudinal EM waves, although TM and TE ...
0
votes
1answer
105 views

How do I create a direct current with a magnet? The magnet is not to be moved in the direction of the wire [closed]

How do I create a direct current with a magnet? The magnet is not to be moved in the direction of the wire. In fact I'm looking for the contrary to the drawing from ...
0
votes
0answers
45 views

Why are magnets attracted to negative side in battery

I have been experimenting with magnets, and built an Homopolar motor however it works but the magnet only attracts the negative side of the AA battery (the flat side of a battery) which I thought was ...
0
votes
2answers
64 views

How is the direction of Magnetic/Electric Lines of Force Known?

It is shown that the direction of magnetic line is from north to the south and that of the electric line is from positive to negative. How do we/scientists know that the imaginary lines of force or ...
0
votes
1answer
46 views

How are the E and B fields inside a coaxial cable related to the current and voltage?

Conceptually, I understand that coaxial cables operate in a TEM mode due to the central conductor, and hence the electric field is directed radially outward from the voltage $V_0$ at the centre of the ...
1
vote
2answers
44 views

Energy of an EM Wave and its temperature and amplitude

I'm trying to understand why classical physics fails to explain black body radiation. I'm confused. According to Boltzmann, energy calculation for em wave is based on temperature. According to ...
2
votes
2answers
61 views

Speed of light in different parts of the universe

Do we have enough evidence to claim that speed of light remains the same at 'c' even at the most distant parts of the visible universe?
2
votes
1answer
100 views

How to transform material permittivity tensor from Cartesian coordinates to another orthogonal coordinate system?

I have a material specified by a permittivity tensor written in Cartesian coordiantes: $$\begin{pmatrix} \epsilon_{xx} & \epsilon_{xy} & \epsilon_{xz}\\ \epsilon_{yx} &\epsilon_{yy} ...
1
vote
0answers
23 views

How to isolate and verify the source of optical absorption/effects?

This is similar to my other question, but not the same -- that one was about the energy ranges of various absorption mechanisms, and this one is more about experimental techniques to find them. Let's ...
0
votes
0answers
16 views

Transmission Line above infinite plane connected by impedance line - Is my drawing correct?

Okay, I was doing a question on transmission lines. The setup is a wire placed at distance $d$ above an infinite conducting plane. The impedance of such a line is $Z_0$. Then there is an impedance ...
1
vote
1answer
44 views

Electricity voltage & current [closed]

Why does current return to its source?
1
vote
0answers
25 views

If lead's electron configuration ends with 6p$^2$, shouldn't it be paramagnetic? [duplicate]

Doesn't lead, according to its electron configuration, have unpaired electrons? Yet why isn't it paramagnetic?
2
votes
3answers
71 views

At an instant, does a system of gravitational charges exhibit equivalent behavior to a time-reversed system of like electric charges?

Question: In principle, does a system of gravitational charges exhibit equivalent behavior to a time-reversed system of like electric charges? (At a single instance in time?) Additional Notes: I am ...
-3
votes
1answer
81 views

Maxwell equations [closed]

$$\oint B.dl = \mu_0\left(I+\epsilon_0\frac{\partial\Phi_E}{\partial t}\right)$$ Please explain the applications , and implications of the modified Ampere's circuital law with Maxwell's addition. ...
2
votes
0answers
33 views

Evaluate singularity in numerical iterative physical optics integral

My goal is to implement a code to numerically compute the radar cross section (RCS) of an open-ended PEC cavity by the approach of "iterative physical optics" [1]. The idea is to iteratively compute ...
0
votes
0answers
25 views

Beat like Interaction with electromagnetic waves

So I was reading earlier on this website and I came across some question similar to this but I want to lead it Into a different direction. I understand that two interacting superposition waves (that ...
0
votes
1answer
86 views

Why is the magnetic field stronger at the edges of a bar magnet?

I have been performing an experiment at school in which I test the force on an iron surface from the magnetic field of an electromagnet. The electromagnet has a rectangular iron core. The theory ...
0
votes
1answer
40 views

Constructive Interference of Electromagnetic Waves

So I was wondering if Electromagnetic wave has the same property of interference as normal waves. I understand that both the electric and magnetic parts of the wave would have to be in the same ...
7
votes
4answers
531 views

Can we say there are 2 EM radiation types?

EM radiation seems to come from two different sources: According to the Maxwell, by acceleration of electrons According to the Bohr, by jumping of electrons between energy levels? Are these two, ...
3
votes
1answer
93 views

Solving electromagnetic vector field using the Lagrangian

Given an action of the form \begin{equation}S=-\frac{1}{4}\int d^4x\eta^{\mu\nu}\eta^{\lambda\rho}F_{\mu\lambda}F_{\nu\rho}\end{equation} where ...
2
votes
3answers
123 views

How do electrons actually move in a circuit?

Last year, we were taught about electricity, about how electrons in a closed circuit. But as our teacher had not taught us about electric fields yet, she gave us a simplified model of motion of ...
1
vote
0answers
32 views

Is the dielectric constant of an insulator always positive?

I know there are many examples of metals with a negative dielectric constant at optical frequencies. But what about insulators?
0
votes
0answers
19 views

insufficient electrons in a conductor [duplicate]

We all know that if an electric field is applied across an isolated conductor, then charges are induced at either surface such that the net electric field inside becomes zero. Now if the applied ...
0
votes
1answer
47 views

Understanding frequency of a signal

I'm trying to understand how can one transmit different signals on a same copper wire using different frequencies. How does the electrons actually interact with the frequency? And how does the ...
1
vote
0answers
22 views

Sphere in homogenou magnetic field

I have to find out the magnetic dipole moment of sphere in homogenou magnetic field in the limit $\mu_r\rightarrow+\infty$. I don't know what does the condition $\mu_r\rightarrow+\infty$ mean. Does ...
4
votes
2answers
202 views

How do I actually calculate the Lorentz transformation of a field strength tensor

Say now I have an arbitrary field strength tensor $F$, and I want to boost it according to a Lorentz transformation matrix $(\Lambda)$ The transformation is given by $$ F^{'\mu \nu} = ...
-3
votes
1answer
61 views

why does alternate current attract and direct current repel [duplicate]

Does AC current attract and DC repel our body? If the potential difference remains same will still AC and DC will give us same type of electric shock?
2
votes
2answers
281 views

Is magnetic force non-conservative? [duplicate]

If magnetic field is conservative, then why not the magnetic force? My professor thinks it is non conservative but he couldn't explain to me why?
0
votes
0answers
26 views

Mutual Inductance of co-planar (but not concentric) loops

Two small wire loops, each with radius b, are placed a distance $d >> b$ apart. The loops are oriented as shown below; i.e., both loops lie in the x-y plane. Each loop carries the same current ...
1
vote
1answer
56 views

What are 'two way' magnets and how do they work?

Thomas & Friends Take-n-Play series connect to each other via something described as 'two way' magnets: the new models use special 'two-way' magnets As a parent of an owner of two engines of ...
0
votes
2answers
85 views

Does a simple copper wire with an AC current create EM waves?

I want to know if a household AC current flowing through a simple copper wire will radiate EM waves? If yes, up to what range and can they be called radio waves?
2
votes
2answers
53 views

Why is this not a violation of parity invarance for EM

I read that Wu's experiment illustrates that parity violation is possible for weak processes. In that experiment, when Co-60 undergoes beta decay, the emitted electrons come out opposite to the ...
1
vote
1answer
54 views

Finding speed of light by $c=f\lambda$?

When considering EM radiation as waves it is said that it is electric and magnetic fields that oscillate with time. Therefore $f$ is not frequency of distance but of electromagnetic fields. I have ...
1
vote
1answer
75 views

Definition of Electromagnetic field?

What is the Electromagnetic field at a given point in space due to a point charge being accelerated non-uniformly? Is there a single equation that can give me the electromagnetic force experienced by ...
0
votes
0answers
20 views

The speed of electrons moving in different medium

Can one have a simple (dimensional-analysis) model to evaluate the speed of electrons moving in: (1) a copper wire (2) a silver wire (3) a gold wire (4) a semiconductor wire let's use meter over ...
0
votes
0answers
44 views

How does QED explain magnetism?

I understand how QED explains, for example, Coulomb's law. But how does it explain the behavior of two bar magnets whose N and S poles attract one another?
3
votes
0answers
45 views

Attraction and repulsion of electron spin ups and electron spin downs

Alright, we know that copper is a diamagnetic material, which has paired electrons. These paired electrons have different spin. I'm specifically interested in what is going on with the electrons in a ...
2
votes
1answer
51 views

What does it mean for an electromagnetic structure to be resonant?

There are many electromagnetic structures used in microwave engineering and EM devices. For example, patch antennas, metamaterials made from unit cells, etc. When they design structures like patch ...
3
votes
1answer
206 views

Why my simple electromagnetic experiment does not work?

I make a setup (see attached picture). ONE coil (1" diameter x ~120 turns), which is separated with a gap, is mount on two sides. Each side has an iron rod (1" diameter x 6" long) to increase the ...
0
votes
2answers
55 views

motion of an electron near a conducting wire [closed]

An electron is ejected from the surface of a long thick straight conductor carying a current, initially in direction perpendicular to the conductor. The electron will: a) ultimately return to the ...
1
vote
0answers
34 views

What would happen if…? (Scenarios involving a ball in an electric field) [closed]

First I shall define two table tennis balls: Ball $A$ is coated with a conducting material and ball $B$ is an insulator. Then I'll define two scenarios: Scenario $I$ is a ball held from a ...
1
vote
0answers
25 views

Difference between action-at-a-distance and a field according to Maxwell?

My question is more on a historical note that involves Maxwell’s equations. Besides the information that I have obtained from textbooks, I am mainly getting it from History of Maxwell's Equations and ...
0
votes
1answer
44 views

Can an electron change direction in a conductor?

Can an electron change direction in a conductor? Or is it restricted to do so? Why can't it change direction do to the atoms of the conductor itself? Why if the change in the electron's direction ...
0
votes
1answer
16 views

Deflection of magnetic compass sorrounded by alternating poles

What happens to the deflection of the magnetic compass if it is surrounded by south poles and north poles in alternating direction of a magnet around it in a circular pattern. Will it be deflected in ...
1
vote
2answers
28 views

What will happen to a solenoid with a bar magnet core?

Suppose I wrap wire around a bar magnet, creating a solenoid such that the poles of a bar magnet and the poles of solenoid are opposite to each other. If I were to hold a compass near one side, which ...
0
votes
3answers
74 views

What will happen to compass with north all around it?

If I keep a compass with bar magnets all around it, all of equal strength and a compass in a center then what will happen? Will the compass start rotating?
0
votes
1answer
47 views

What is the mechanism for the production of the electromagnetic radiations due to accelerated charge particles?

I have recently read in Griffiths that when a charge particle get accelerated the electromagnetic field associated with it get " ditatched " from it and this detatched electromagnetic field is what we ...
0
votes
0answers
11 views

Zero field cooled / field cooled susceptibilities

I'm studying magnetic properties of nanoparticles in a liquid carrier and trying to understand better zero-field-cooled/field-cooled curves. We use the Stoner–Wohlfarth model and Chantrell ...
0
votes
2answers
94 views

Prerequisites for Griffiths electrodynamics [duplicate]

I want to start reading Griffiths electrodynamics during my holidays. But I am not sure of the math I need to know to start reading and understand the text thoroughly. So any advice would be ...