Tagged Questions
0
votes
2answers
63 views
Violation of Newton's 3rd law
I'm just expressing my guess.
Let two particles A and B experiences forces $F_1$ and -$F_2$ between them and let guess also there are two observer, one is stationary and other is moving with ...
3
votes
3answers
165 views
Energy conserved… or not? Confused!
I am confused. Could someone kindly explain what's going on in this question?
A particle of mass $m$ and charge $e$ moves in the $x,y-$ plane. There is a constant magnetic field $B$ that points in ...
2
votes
1answer
101 views
How Special Relativity causes magnetism
So my physics teacher assigned us an article about how special relativity causes magnetism in a wire with a current, even with the low drift velocities of electrons in a current.
It seemed that the ...
1
vote
0answers
43 views
Solving the equation of relativistic motion
How does one solve the tensor differential equation for the relativistic motion of a partilcle of charge $e$ and mass $m$, with 4-momentum $p^a$ and electromagnetic field tensor $F_{ab}$ of a constant ...
-4
votes
3answers
176 views
There must be free positive charges, moving oppositely to electrons for the wire with current to stay neutral
All popular expositions (e.g. these ones) of relativistic electromagnetism claim univocally that electrons in motion become more dense due to the speed. They teach that Lorentz contraction of charges ...
2
votes
4answers
252 views
Relativistic origin of magnetic field
There is an explanation in the Wikipedia. Unfortunately the article is quite verbose and doesn't clearly explain why both positive and negative charges vary density even if only one is moving.
It is ...
1
vote
2answers
142 views
Relativistic charge density contraction in a closed loop
I have heard that magnetism is a relativistic effect of electricity. The law says that charge is conserved, only distances are shrunk. So, I cannot add more charge to increase density. When we have an ...
2
votes
1answer
49 views
Field Tensor and classical limits
I would be very grateful if someone would kindly explain this generalization of the Lorentz force law to the special relativity domain. Please bear with me.
Classically, the Lorentz force law is ...
1
vote
1answer
88 views
Retarded time Lienard Wiechert potential
In a potential which needs to be evaluated at the retarded time, is this the time which represents the actual time the "physics" occurred? So $t_{\text{ret}}=t-\frac{r}{c}$, not just because it may be ...
-1
votes
2answers
120 views
Do objects have energy because of their charge?
My gut feeling tells me things should have energy because of their charge, like they have energy because of their mass.
Is this possible? Has it been shown? If not then what is missing to make such ...
2
votes
1answer
70 views
Properties of the Faraday tensor for constant fields
I'm doing a special relativity past exam paper and have got caught up with something that I hope someone can help me with!
I have to show that for constant fields, the magnitude of A, the ...
1
vote
1answer
118 views
Showing Lorenz gauge is satisfied in retarded potential - vector calculus
I am trying to show that $\nabla\cdot \vec{A}=-\mu_0 \epsilon_0 \frac{\partial V}{\partial t}$
$V=\frac{1}{4\pi\epsilon_0}\int \frac{\rho(\vec{r}',t_r)}{r}d\tau'$
$\vec{A}=\frac{\mu_0}{4\pi}\int ...
4
votes
2answers
129 views
Relativistic Lorentz force law
If we consider the the relativistic Lorentz force law:
$$\frac{d}{dt} (m\gamma \vec{u})=e(\vec{E}+\vec{u} \times \vec{B})$$
How can we deduce:
$$\frac{d}{dt} (m\gamma c^2)=e \vec{E} \cdot \vec{u}$$
...
1
vote
1answer
90 views
Faraday's Law and Galilean Invariance
In Jackson's text he says that Faraday law is actually:
$$
\oint_{\partial \Sigma} \mathbf{E} \cdot \mathrm{d}\boldsymbol{\ell} = -k\iint_{\Sigma} \frac{\partial \mathbf B}{\partial t} \cdot ...
4
votes
4answers
315 views
Can a photon get emitted without a receiver?
It is generally agreed upon that electromagnetic waves from an emitter does not have to connect to a receiver, but how can we be sure this is a fact? The problem is that we can never observe non ...
3
votes
1answer
78 views
How would I perceive a purple ball when traveling at relativistic speeds
I have a 'thought experiment' which I'd like to ask about.
I was thinking what speed I would have to drive towards a crossing to see a red light as a green light - pretty easy, using the doppler ...
1
vote
0answers
148 views
Does Mansuripur's Paradox involve fictitious charges?
Mansuripur's Paradox involves a magnet moving at relativistic speeds in an external electric field.
Additional: thanks to Retarded Potential, who found the original paper.
If I understand correctly, ...
8
votes
3answers
322 views
Where's the energy in a boosted capacitor?
Suppose I look at a parallel plate capacitor in its rest frame and calculate the electrostatic energy, $E$.
Next, I look at the same capacitor in a primed frame boosted in the direction perpendicular ...
1
vote
1answer
93 views
Does special relativity unify the two phenomena at the base of Faraday's flux law (was Feynman wrong in this case)?
Consider Faraday's flux law for the EMF generated in a conductor loop:
$$ \varepsilon = - \frac{d \phi}{dt},$$
where $\varepsilon$ is the EMF, and $\phi$ is the magnetic flux through the loop.
...
2
votes
2answers
196 views
D'Alembert operator and special relativity
We are currently covering special relativity in the theoretical physics lectures where we defined:
$$
\mathrm ds^2 := \mathrm dt^2 - \mathrm dx^2 - \mathrm dy^2 - \mathrm dz^2
$$
In Road to Reality, ...
8
votes
3answers
332 views
Why do Maxwell's equations contain each of a scalar, vector, pseudovector and pseudoscalar equation?
Maxwell's equations, in differential form, are
$$\vec\nabla\cdot\vec{E}=~\rho/\epsilon_0,$$
$$\vec\nabla\times\vec B~=~\mu_0\vec J+\epsilon_0\mu_0\partial\vec E/\partial t,$$
$$\vec\nabla\times\vec ...
-1
votes
1answer
734 views
Violation of Newton's 3rd law and momentum conservation
Why and when does newtons 3rd law violate in relativistic mechanics? Check this link http://www.animations.physics.unsw.edu.au/jw/Newton.htm.
4
votes
1answer
182 views
What do I see if I move quickly past a charge surrounded by iron filings?
This might be a straightforward exercise, in which case I apologize. Suppose I surround a charge by iron filings initially oriented in some fixed direction, and I then move past the charge at an ...
5
votes
4answers
181 views
The necessity of the B field
It is fairly easy using basic special relativity to arrive at the conclusion that the magnetic force effect on nearby charges of wires carrying currents on nearby charges is only due to the length ...
4
votes
2answers
466 views
Does special relativity make magnetic fields irrelevant?
I've heard that special relativity makes the concept of magnetic fields irrelevant, replacing them with relativistic effects between charges moving in different velocity frames. Is this true? If so, ...
0
votes
1answer
85 views
Wavefronts and phase velocity faster than $c$
Lets assume we have parallel wavefronts in a glass of water:
and we put an inclined rod on the water surface:
related to a very small inclining, Vy velocity is greater or much greater then Vx ...
3
votes
2answers
192 views
Magnetic paradox in relativity?
Let 2 electrons A and B be moving parallel with constant velocity $c/10$ in (near) vacuum without a strong gravity field (where $c$ is speed-of-light).
A and B create an electromagnetic field that is ...
3
votes
3answers
480 views
Maxwell equations invariant under Lorentz transformation but not Galilean transformations
Why Maxwell equations are not invariant under Galilean transformations, but invariant under Lorentz transformations? What is the deep physical meaning behind it?
6
votes
1answer
255 views
Is there a strong force analog to magnetic fields?
In special relativity, magnetism can be re-interpreted as an aspect of how electric charges interact when viewed from different inertial frames.
Color charge is more complex than electric charge, but ...
3
votes
1answer
545 views
Darwin term and Zitterbewegung
I've noticed that in the discussion of the fine structure of Hydrogen atom standard QM texts claim that the Darwin term, which corrects energy of $\ell=0$ (or $s$-) states only, is related to the ...
1
vote
2answers
225 views
Using Lorentz Invariance of Charge To Calculate Current Density
I'm attempting a problem from Zwiebach: A First Course in String Theory and am completely stuck. Could anyone give me a hint? The problem is as follows.
Consider $S$, $S'$ two Lorentz frames with ...
2
votes
2answers
145 views
Applying $\nabla\times\mathbf{B} = \mu_0\mathbf{J}$ in the presence of magnetic shielding
2012-06-13 - Revised question in experimental format
(This is a thought experiment for which RF experts may have an immediate answer.)
I'll assume (I could be wrong) the possibility of creating a ...
5
votes
3answers
536 views
Trouble with the Lorentz law of force: Incompatibility with special relativity and momentum conservation?
In Physical Review Letters, there was a paper recently published:
Masud Mansuripur, Trouble with the Lorentz Law of Force: Incompatibility with Special Relativity and Momentum Conservation, Phys. ...
1
vote
1answer
68 views
Perpendicular Fields and Equations of Motion
I have the following problem to solve:
A particle of mass $m$ and charge $e$ moves in the laboratory in crossed, static, uniform, electric and magnetic fields. $\mathbf{E}$ is parallel to the ...
7
votes
2answers
439 views
The equivalent electric field of a magnetic field
I know that Lorentz force for a charge $q$, with velocity $\vec{v}$ in magnetic field $\vec{B}$ is given by
$$\vec{F} =q \vec{v} \times \vec{B}$$
but there will exist a frame of reference where ...
4
votes
2answers
527 views
Can a static magnetic field turned into a static electric field? or vice versa?
Consider some positive charge that is distributed uniformly over a very long line along the z-axis.
If I am stationary with respect to the line then there is only static electric field which has ...
4
votes
1answer
289 views
Lorentz force law in Newtonian relativity
I know that in special relativity Electric and Magnetic fields mix together in different reference frames, but my question is about classical mechanics.
It seems weird to me is that the Lorentz Force ...
2
votes
4answers
395 views
How is this classical “paradox” resolved in electromagnetism?
A magnet and a coil move relative to each other. In the frame of reference of the magnet, there is a magnetic field and consequently a force acting on the charges in the coil according to the Lorentz ...
2
votes
2answers
267 views
How to measure faster than light electric energy?
According to relativity,nothing can break light barrier.But a recent preprint shows energy transmission of commercial electric power (f=60Hz) is faster than light. (It is not the drift velocity of ...
2
votes
2answers
204 views
Must the action for a relativistic charge be a Lorentz scalar?
Page 580, Chapter 12 in Jackson's 3rd edition text carries the statement:
From the first postulate of special relativity the action integral must be a Lorentz scalar because the equations of ...
9
votes
2answers
350 views
Essential background for QFT study
The preface to Mark Srednicki's "Quantum Field Theory" says that to be prepared for the book, one must recognize and understand the following equations:
$$\frac{d\sigma}{d\Omega} = ...
1
vote
0answers
111 views
Show that the electric field E in the system at rest is $E=\frac{Q}{4 \pi \epsilon_0 \sqrt{(x^2+y^2+z^2)^3}} (x,y,z)$ [closed]
A body point charge $Q$ moves in relation to the reference system $\Sigma$ according to the law of motion $x(t)=v_0 t$, $y(t)=0$, $z(t)=0$.
4
votes
2answers
111 views
Can D and H form an 'in materials' version of the electromagnetic tensor?
In analogy to the electromagnetic tensor, with the components defined as the electric field $E$ and magnetic field $B$ as such:
$F^{ab} = \begin{bmatrix}
0 & -E_x/c & -E_y/c & -E_z/c \\
...
2
votes
1answer
1k views
Relativistic charged particles in a constant uniform magnetic field
How can i derive the dynamic of a relativistic charged particle in a uniform magnetic field $B=(0,0,B)$?
4
votes
1answer
400 views
Calculate the electric field of a moving infinite magnet, without boosting
Consider a rectangular slab of permanently magnetized material. The slab's dimensions are $L_x$, $L_y$, and $L_z$, and the slab is uniformly magnetized in the $\hat{x}$-direction. The slab is not ...
2
votes
1answer
367 views
Magnetic moment of relativistic rotating ring
Let's consider rotating charged ring. Theoretically mass of this ring has no limit as rotation speed increases. So what about magnetic moment of the ring? Is it limited by the value of speed of ...
7
votes
3answers
1k views
Are Classical Field Theory and Quantum Mechanics of a single particle (nonrelativistic or “classical”) limits of Quantum Field Theory?
Recently I talked about QFT with another physicist and mentioned that the Quantum Field Theory of a fermion is a quantisation of its one-particle quantum mechanical theory. He denied this and ...
19
votes
2answers
633 views
Covariant Description of Light Scattering at a fastly rotating Cylinder
Let us consider the following Gedankenexperiment:
A cylinder rotates symmetric around the $z$ axis with angular velocity $\Omega$ and a plane wave with $\mathbf{E}\text{, }\mathbf{B} \propto ...
23
votes
9answers
3k views
Can Maxwell's equations be derived from Coulomb's Law and Special Relativity?
As an exercise I sat down and derived the magnetic field produced by moving charges for a few contrived situations. I started out with Coulomb's Law and Special Relativity. For example, I derived the ...
1
vote
2answers
434 views
Is there an explicit angular momentum in Maxwell equations?
Electromagnetism implies special relativity and then the universal constant "c". And if we set c=1, the coupling constant has units of angular momentum (so in relativistic quantum mechanics we divide ...
