Questions tagged [electromagnetism]
The classical theory of electric and magnetic fields, both in the static and dynamic case. It also covers general questions about magnets, electric attraction/repulsion, etc. Distinct from electrical-engineering.
19,234
questions
1
vote
2
answers
168
views
How to solve Relativistic Lorentz Force equation if $\gamma$ is not constant?
I am trying to numerically obtain the trajectory of an electron inside a periodic magnetic field $\mathbf{B}$, taking into account that the relativistic factor $\gamma$ is not a constant (the electron ...
0
votes
1
answer
258
views
Motor Effect Experiment
I recently saw an demonstration (image below) where the motor effect was being shown. They used the fact that forces come in pairs (Newton's third law) and so when current goes through the copper rod, ...
0
votes
0
answers
46
views
A question on perturbed flux function
Given a magnetic field $\mathbf{B}=B_{0}\left(\dfrac{xz}{z_{s}^{2}},\dfrac{yz}{z_{s}^{2}}, 1-2\left( \dfrac{x^{2}}{r_{s}^{2}}+\dfrac{y^{2}}{r_{s}^{2}}\right) -\dfrac{z^{2}}{z_{s}^{2}}\right)$ with the ...
2
votes
1
answer
293
views
Materials to complement "Interacting Electrons and Quantum Magnetism" by Assa Auerbach
Does anyone know of any material, such as lecture notes from a university, that can complement the sometimes brief chapters of the book "Interacting Electrons and Quantum Magnetism" by Assa Auerbach?
...
0
votes
1
answer
262
views
How does changing the angular frequency ω of the generator affect the current flowing in the circuit and the power transferred to the electric motor?
When an electric motor is used with an electric generator, the situation can be viewed as an RLC circuit where the generator is an AC power source. The source produces a sinusoidal AC voltage with an ...
2
votes
1
answer
418
views
Eddy current brake with superconductor
There are eddy current brakes used with metal plates to stop trains. It converts kinetic energy of the metal plate to heat via eddy current on it. So what if we have a superconducting metal plate and ...
1
vote
5
answers
4k
views
What's the difference between conduction current density and source (impressed) current density in an $RC$ circuit?
My electromagnetics textbook has a picture of an $RC$ circuit with a current source.
As you can see, there are three current density vectors, $J_i$, $J_c$, and $J_d$. The book labels them as follows:
...
0
votes
1
answer
37
views
What is the impressed current density? [duplicate]
I don't have a too solid background for physics and am reading some engineering books of electromagnetics. What is the impressed current density here? I think it is Ohm's law but couldn't find its ...
0
votes
4
answers
44
views
Comparing Electric Potential Energy of two Charges
I do not know what I am missing here and would appreciate a little help in figuring out the flaw in my logic. I have a row of positive charges and a row of negative charges as shown in the image above....
0
votes
0
answers
16
views
Effects of Localized Medium Changes on Field Propagation
I've studied various theories related to fields. These theories often include equations describing how the activity of a source is transmitted to other locations. The properties of the medium ...
2
votes
1
answer
351
views
Velocity gained as a metal object approaches a magnet
I need to find the Kinetic Energy gained as a steel bearing ball approaches a Neodymium magnet. I have the value for the magnetic flux density of the magnet, now I need to find a way to calculate the ...
3
votes
3
answers
77
views
Why the $T_1$ recovery & $T_2$ decay are independent?
In MRI, I was thinking that the decrease in transverse magnetization results in the recovery of longitudinal magnetization.
However, recently, I found it was wrong. I saw a diagram
(McRobbie 2014. ...
2
votes
2
answers
922
views
How do you convert from Townsend Unit $\rm Td$ to $\rm kV/(cm bar)$?
I have found a conversion online which says 1Td = 2.829 V/(cm Torr) and 1Torr = 0.001332 bar and with this;
1Td = 0.3768 V/(cm bar)
However from literature for SF6;
362Td = 86.3 kV/(cm bar) where they ...
0
votes
1
answer
47
views
Most generic form of refractive index tensors
The refractive index of a material is in general a $3x3$ tensor (as in the case of birefringent crystals). From literature, it seems that in the case of transparent crystals, this tensor is in general ...
1
vote
0
answers
33
views
Rotating Tank of Charged Liquid
Consider a long rectangular tank of dimensions a×b, where a≫b, that is rotating at a constant angular velocity and filled with an incompressible charged fluid. How would one find an equation ...
2
votes
1
answer
645
views
Can a satellite generate electricity by using a planet's magnetic field? [duplicate]
I am entering AP Physics E&M and don't have much knowledge about electricity but always had an idea based on my limited knowledge.
If a satellite had a metal coil inside of it, wouldn't it have an ...
1
vote
2
answers
43
views
Straight wire in moving uniform magnetic field induced emf
My question is a follow-up to this one.
The green dotted line is the arbitrary loop which is constructed in the calculation of emf in the wire of length L. x is a variable which can be changed to ...
2
votes
1
answer
1k
views
Doppler Cone: What exactly is it?
I'm trying to understand Synthetic Aperture Radar (SAR). It appears that it makes use of what's called a "Doppler cone". I understand Doppler frequency shifts of light, but I'm not sure what the cone ...
0
votes
3
answers
100
views
What is the net macroscopic electric field at any point inside a dielectric?
This question is based on section 4.2.3 of Introduction to Electrodynamics by David J. Griffiths (Third Edition).
Consider a point $\vec{r}$ inside a dielectric where we are interested in finding the ...
2
votes
2
answers
199
views
Induced electrical field of infinite straight current carrying wire
I'm kinda confused about the law of induction of a straight wire.
Suppose I have an infinite (infinitely long and thin) wire along the z-axis with current $I=I_0 \cos(\omega t) \, e_z$. The magnetic ...
0
votes
1
answer
338
views
Does charge carrier concentration vary with magnetic field (due to Hall effect)?
I'm writing up an experiment on the use of the Hall effect to determine charge carrier concentration for n-doped Germanium. Which initially led me to believe that the concentration is a constant for a ...
2
votes
2
answers
228
views
No EMF generated on a loop lying outside changing $\vec B$ (but $\vec E ≠ 0$)
If we establish a changing magnetic field in a region of space, circular electric field lines are induced. This electric field extends even after we exit the region of the magnetic field. If a closed ...
1
vote
1
answer
46
views
Is it possible for both electric and magnetic fields to have longitudinal component in a rectangular waveguide?
I know a rectangular waveguide cannot support TEM waves, but supports TE and TM waves. In the TE mode, $E_z=0$ and in the TM mode, $H_z=0$ (where propagation direction is along the $z$-axis). I want ...
0
votes
1
answer
35
views
Volume distribution of charge in a wire in a DC circuit
According to this and several other articles some amount of charge in a DC circuit distributes itself on the surface of the conductor, making the electric field inside parallel to the said surface.
...
1
vote
1
answer
52
views
Confusion regarding phase
As far as I know about phase if the phase difference between two waves is positive, the former is leading..and the latter is lagging. Then why has D J Grifith stated this?
If the phase of the magnetic ...
1
vote
1
answer
1k
views
Explanation of crystal formation in a Fitzroy's storm glass with the change in weather conditions
I was recently reading about Admiral Robert FitzRoy's storm glass and how it was used to predict the weather conditions based on the formation of camphor crystals in a sealed glass tube containing ...
0
votes
1
answer
532
views
Magnetic force acting on a current carrying wire
I am a high school student and I would like to know why in a magnetic field the Force, $F$, is equal to $BIL\sin(\theta)$, where $\theta$ represents the angle between the magnetic field and the ...
1
vote
1
answer
61
views
I don't understand Green's derivation of the Laplace/Poisson equation inside an electrically charged body
I am currently reading George Green's "An Essay on the Application of Mathematical Analysis to the Theories of Electricity and Magnetism"Green's essay to gain some insight into the original ...
0
votes
1
answer
663
views
Magnetic field of coaxial cylindrical capacitor
I have a coaxial cylindrical capacitor as shown, with inner radius a and outer radius b.
The potential difference across both cylinders is V. I need the magnetic field everywhere when the inner ...
2
votes
2
answers
96
views
Current loop and electromagnetic energy
Take a fixed circular loop of wire in a uniform magnetic field. As far as I can tell, the work we have to do to accelerate the electrons in the wire so a particular current is attained is independent ...
3
votes
2
answers
156
views
The puzzling interaction between an anapole moment and external fields
Consider an electrical current distribution with only an [anapole, or toroidal moment] but no electrical or magnetic multipole moments, like this current on a torus:
Its magnetic field is completely ...
1
vote
0
answers
50
views
When refrence frame has the same velocity of electron the we observe that electron seems like satatic. Then why it produces megnetic field. And why it [closed]
When refrence frame has the same velocity of electron the we observe that electron seems like satatic. Then why it produces megnetic field.
0
votes
1
answer
484
views
Larmor Frequency for Spin Transition
http://hyperphysics.phy-astr.gsu.edu/hbase/magnetic/larmor.html
Consider the process of Larmor precession of the magnetic moment associated with the spin angular momentum of an electron inside a ...
1
vote
1
answer
82
views
Why is potential directly proportional to charge?
In my textbook, it’s written that conductors' charge is directly proportional to voltage and they used this idea to develop the concept of capacitance. How can you prove this for any conductor?
1
vote
1
answer
445
views
Why would the peak strength of the magnetic field of an AC-electromagnet be higher than the peak field strength of a DC-electromagnet?
Elsewhere on Stack Exchange several people have said that the average, mean or RMS value of the magnetic field of an AC-electromagnet would be about the same, or slightly lower than, a DC one. But, ...
0
votes
0
answers
22
views
Why don't static magnets attract copper wires? [duplicate]
I have a few simple magnets, like 1x2 cm (probably neodymium) magnets and similar smaller circular ones (similar to fringe magnets). They attract a (probably zinc or iron) wire: the wire is ~dark-grey,...
3
votes
2
answers
481
views
Moving charge to define magnetic field
Why charged particle has to be in motion to define magnetic field?
Will magnetic force exert any force on a static charge? (as in the static test charge in electric field)
A line from my book reads-
"...
0
votes
0
answers
25
views
The absorption of infrared light for regular materials, like fabric wallets backpacks and clothes
I work as a brand partner for a company that produces a patch which strengthens the production of stemcells in the body.
The patches are activated with the help of the bodys own infrared radiation.
I ...
1
vote
1
answer
109
views
Electric field under gravity
For a spherically symmetric mass m of radius r and charge q, how does the electric field vary with distance d from the center where d > r.
Does it still vary as $\dfrac{1}{r^2}$ or is there a ...
1
vote
1
answer
329
views
Lienard-Wiechert Potentials Issue
I have had some difficutlies in trying to obtain the Lienard-Wiechert potentials of a moving "point charge" and would greatly appreciate any help in this matter. I will adopt the definition ...
1
vote
0
answers
82
views
How do I find magnetic force between two particles? [duplicate]
First, for a charge $q_1$ with position $\vec{s}_1$ and velocity $\vec{v}_1$, the magnetic field caused by the particle at position $\vec{s}_2$, the equation I've found is
$$\vec{B} = \frac{\mu_0}{4\...
5
votes
1
answer
287
views
Is there a (semiclassical) electric field operator?
So I come from a chemistry background, where the electronic structure of atoms and molecules is central. For practical purposes, we usually work with a charge density operator
$$ \hat{\rho}(r) = q \...
0
votes
1
answer
211
views
Is the charge density value in the electromagnetic wave equation necessarily equal to zero?
The transmission space of electromagnetic wave is divided into source free and source region. In the case of source region, the current density is not equal to zero because the electromagnetic wave ...
1
vote
2
answers
755
views
Why do we need an objective lens in a scanning electron microscope?
I've been studying scanning electron microscopes quite a bit but can't seem to get my head around why we need objective lenses.
On paper I don't see a reason, if we would want to focus the electron ...
0
votes
1
answer
67
views
Can an oscillatory field produced by a time-dependent charge distribution fall off faster than $1/r$?
An electric charge has a field that decays at large distances like $1/r^2$. A charge distribution with total charge zero, but with a nonvanishing dipole moment, has a field that decays at large ...
0
votes
2
answers
307
views
Biot-Savart Law
Today we started learning about Biot-Savart law. While deriving the formula, our professor listed out a bunch of relations, which have been experimentally determined,
->dB is directly proportional to ...
0
votes
0
answers
19
views
Would it be possible to use Diamagnetic force working along with gravity to make a sort of two-way stream?
I was wondering if it would be possible for someone to generate some sort of two-way stream by positioning a strong NdFeB magnet below an upward pointing tube containing something like a Bismuth or ...
0
votes
1
answer
616
views
Location of high and low potential points in motional emf
Okay so in the above image the semi circular loop is rotated and a sector of it is introduced into the magnetic field.
Questions:
I know the magnetic field is constant so no non conservative ...
0
votes
2
answers
57
views
Growth of Current in an Inductor Connected Across a Battery [duplicate]
When baterry is connected across inductor with no resistance in circuit, won't the current flowing through it be zero, as inductor back emf will counteract the effect of potential difference due to ...
8
votes
4
answers
10k
views
Behavior of the Electric- and Magnetic-field under time reversal and parity
The behavior of the electric- $\mathbf{E}$ and the magnetic-field $\mathbf{B}$ und time reversal and parity can be calculated in different ways.
My first solution is to study the transformation ...