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16 views

Induced emf in a circular conducting wheel

Consider a conducting wheel with $N \in \mathbb{N}$ spokes which is completely in a homogenous magnetic field $\vec{B}$ perpendicular to the wheel plane. ...
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0answers
12 views

Penning Trap Simulation

I'm currently working on a particle tracker and I would like to implement a Penning trap. I think I might have a problem with the field of the electrical quadrupole. My idea was to place 2 dipoles and ...
8
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2answers
479 views

Trouble understanding the Bohr model of the atom

In this article it says: The electrons can only orbit stably, without radiating, in certain orbits (called by Bohr the "stationary orbits") at a certain discrete set of distances from the nucleus. ...
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3answers
2k views

Can two electrons get ever so close as to touch each other?

My friend and I were studying for our EM test when we started to think about what happens to the electric field near an infinite line of charge. $$E = \frac{\lambda}{2\pi\rho\epsilon_{0}}$$ As you ...
3
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1answer
63 views

Tensor notation

I'm trying to understand the Maxwell Stress tensor notation. I'm given that each element in the tensor is given by ...
1
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1answer
62 views

Using Ampere's Law without Right-Hand-Rule to derive an expression for the magnetic field around a current

I'm a little confused over the textbook example of applying Amperians to get the magnetic field around a current. I understand we take a loop which shares the rotational symmetry of the wire (a ...
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2answers
40 views

Electric field of spherical charge distribution

When solving the equation $$\boxed{ {1 \over r^2}{\partial \left( r^2 E_r \right) \over \partial r} + {1 \over r\sin\theta}{\partial \over \partial \theta} \left( E_\theta\sin\theta \right) + {1 ...
2
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2answers
120 views

Textbook on classical E&M in curved spacetime

Can anyone recommend a good reference for classical electrodynamics that goes over electrodynamics in curved spacetime that doesn't assume much knowledge of GR -- that is it builds up the tensor ...
2
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1answer
78 views

Charge vs Charge Density in classical electrodynamics

What is assumed to be a more fundamental physical quantity in classical electrodynamics. The charge density as a scalar field or the physical entity charge.
2
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1answer
43 views

Demagnetisation by throwing a magnet

I tried to answer this question in a book about electrodynamics: How to demagnetise a permanent magnet, ie. described by $ D_T$ change into described by (0,0) I figured out about heating it up ...
4
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2answers
128 views

Instantaneous Coulomb interaction in QED

It seems I am stuck with a (at a first sight) trivial problem. It's from the "Quarks and Leptons" (Halzen, Martin) book page $141$, where one considers the following integral: $$\tag{1} T_{fi} = ...
1
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1answer
65 views

Relating Quantum Mechanics to Classic Electromagnetism [duplicate]

I've been directed to a few articles, and I am sure there is a related post, but can someone explain the procedure by which we can view classic electromagnetism through quantum mechanics? Indeed we ...
4
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2answers
340 views

Aharonov–Bohm effect on a non-contractible manifold

The Aharonov–Bohm effect shows the vector potential $\mathbf{A}$ is more fundamental than magnetic flux density $\mathbf{B}$. However, vector potential is introduced by $$ \nabla \times \mathbf{A} = ...
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0answers
32 views

My model of Conductors in “static” condition - Please analyze

My textbook presents an idealization of a conductor as made up of infinitesimal units of charge and derives results. I was not convinced, so I started thinking of how electric fields are in real ...
1
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1answer
64 views

Angular momentum of light

Can someone explain the classical angular momentum in electromagnetic theory of light? If I shine elliptically polarised em wave on a black disc it rotates. I would like to know how to calculate ...
1
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0answers
56 views

Poynting Vector Volume Integral Inside a Cavity

Given an electromagnetic wave in resonance mode in a vacuum cavity inside a perfect conductor, on the boundary, the parallel component of $E$ field vanishes, and the perpendicular of component of $B$ ...
1
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1answer
148 views

Total Momentum From a Standing Electromagnetic Wave

How does one show the momentum imparted to a perfect conducting resonance cavity (boundary) of any shape by a classical standing electromagnetic wave inside is zero? It should be by conservation of ...
3
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2answers
87 views

Utility of gauge four-potential $A_{\mu}$ (as opposed to electric and magnetic fields ${\bf E}$ and ${\bf B}$) in E&M?

The action for an electromagnetic field with source charges is given by $$S= \int \left\{ \frac{1}{4\mu_0}F^{\mu\nu}F_{\mu\nu} - J^\mu A_\mu \right\}dx$$ By setting $dS=0$ and taking the Lorenz ...
3
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2answers
136 views

Classical Viewpoint on Electromagnetism

Note: This question may be difficult or impossible to answer within the rules of these forums due to its philosophical nature. I will delete the question if I am violating the rules. Onto the ...
3
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2answers
57 views

Showing that Coloumb and Lorentz Gauges are indeed valid Gauge Transformations?

I'm working my way through Griffith's "Introduction to Electrodynamics". In Ch. 10, gauge transformations are introduced. The author shows that, given any magnetic potential $\textbf{A}_0$ and ...
3
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0answers
135 views

Free charge movement in an electric field - including bremsstrahlung

Let us imagine a free, negatively charged object that is in rest and placed in an elecric field of a point positive charge. The positive charge has a huge mass and cannot move, so we consider only the ...
0
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0answers
13 views

Where does $R/\gamma^3$ come from in relativistic E&M?

I am starting to read many papers on electron beam physics; more specifically its motion in a magnet i.e. curved motion. The term $R/\gamma^3$ comes up a lot, but I don't know where they are coming ...
2
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2answers
43 views

Reference on electrodynamics with tempered distributions

Back in my undergrad I had a course on classical electrodynamics where the fields had values in the space of tempered distributions. In this way one could correctly treat self-interaction and ...
0
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0answers
30 views

Polarizable molecule in E-field

If we have a linear molecule with a dipole moment $\mu$ in a static electric field $E$, the potential is given by $V = - \langle \mu,E \rangle$. What is the appropriate equation for the potential if ...
3
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1answer
81 views

A question about the Thomson experiment

Recently, I was studying about Thomson's experiment with cathode rays. My textbook shows it like this. It says: When only electric field is applied, the electrons deviate from their path and ...
0
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1answer
84 views
1
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2answers
92 views

Velocity of a Charged particle in a magnetic field according to Biot-Savart Law

According to Biot-Savart Law, if there is a charged particle in motion, there will be a magnetic field. My question is whether the counterpart of this law also holds true, i.e. if there is a magnetic ...
1
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1answer
33 views

Particle in Oscillating Field

Ignoring quantum effects, what are the dynamics of an electrically charged particular placed with zero initial momentum in an oscillating electromagnetic field, e.g. light?
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4answers
236 views

Why ONLY Maxwell's equations are the basic equations of electromagnetism?

In electromagnetism we say that all the electromagnetic interactions are governed by the 4 golden rules of Maxwell. But I want to know: is this(to assume that there is no requirement of any other ...
0
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1answer
31 views

Determine stationary angular velocity of wheel with circuit in magnetic field

I have a wheel (free to spin around the $z-$axis) with four spokes that is connected by sliding contacts to a circuit with $U_0 = 0,72V$. Also, there is a B-Field parallel to the $z-$axis For the ...
1
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1answer
51 views

Why can we allow the speed of light being infinite in case of Surface Plasmons?

I have a problem with understanding of these sentences: We have indicated in the opening paragraph of the Introduction that surface plasmon polaritons are solutions of Maxwell’s equations in ...
4
votes
2answers
80 views

What is the difference between surface plasmon and surface plasmon polariton?

I'm trying to understand this reading article linked below and I still don't know how to explain this simply, without need to derive everything mathematically. Can someone just write here how do SP's ...
1
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1answer
90 views

Ion Optics: Electric and Magnetic field. A comparison with Light Optics

When we compare ion optics with light optics, normally we consider electric field. For example Snell's law. $n_1\sin\theta_1$=$n_2\sin\theta_2$. When an electron move from one electric potential to ...
0
votes
1answer
25 views

How to account for the huge difference in susceptibility of liquid and gaseous oxygen?

I noticed this while studying magnetic fields in matter from Griffiths' Electrodynamics book. A table is provided in the chapter which shows the materials with their respective susceptibilities. Under ...
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1answer
137 views

Poynting's theorem and escaping particles

I've edited my original question into horrible monstrosity (I apologize to all who spent their time on it). Here is rephrased version which hopefully will be clear. Lets have following model ...
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0answers
34 views

Confused about SI and CGS Units For E/M Energy

I've been looking at some papers on wakefields of electron beams and I am a little confuded about the units. They do not specify whether or not they are in cgs or SI units. Here is a sample equation: ...
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0answers
19 views

Understanding What A Wakefield Describes?

I am trying to understand the some of the properties of wakefields, namely the energy change. So, as a preface I am interested in primarily the wakefield due to electron beams as they progress through ...
8
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2answers
133 views

Counting the number of propagating degrees of freedom in Lorenz Gauge Electrodynamics

How do I definitively show that there are only two propagating degrees of freedom in the Lorenz Gauge $\partial_\mu A^\mu=0$ in classical electrodynamics. I need an clear argument that involves the ...
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1answer
336 views

Recovering all of Maxwell's equations from the variational principle

Whether you can get the first couple of Maxwell equations from a variational principle? In the second volume of the Landau theoretical physics said that it is impossible.
0
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1answer
46 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
56 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
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2answers
120 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 ...
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3answers
66 views

Excitons in metals-do they exist?

Recently I red an article "Surface Enhanced Fluorescence". It is a topical review by Emmanuel Fort and Samuel Gresillon. Here it is: ...
0
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1answer
85 views

Online course on theoretical electrodynamics [duplicate]

I'm looking for good online course for an introduction into theoretical electrodynamics. However, it seems that the MIT opencourseware only contains partial lectures for this topic. Has anyone got a ...
0
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0answers
49 views

Exercise Lorentz Transformations

I have 2 inertial frames, both are in relative motion along the x axis moving with constant velocity $v_x$. It is called with Standard figuration where the Lorentz transformations relate the ...
1
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3answers
136 views

How the electric field or magnetic field itself contain momentum?

I have recently come to know that the electric and magnetic field contain both the translational and angular momenta in it given by some particular formulas at any given instant of the space....But I ...
5
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1answer
175 views

Maxwell's Stress Tensor

What really is the Maxwell Stress Tensor? I understand that it's derived from $$\mathbf {F} = \int _V ( \mathbf E + \mathbf v \times \mathbf B )\rho \ d \tau$$ Griffiths describes this as "total EM ...
1
vote
1answer
47 views

calculating electrodynamic momentum of a dumbbell (consisting of two point charges) in longitudinal motion

I'm working through a paper on momentum in electrodynamics that requires the integration below and would greatly appreciate any help. I'm pretty sure it evaluates to $2/d$ but I can't quite figure ...
1
vote
2answers
66 views

Connection between $\textbf E$ and $\textbf D$ can be non-local ? - Electrodynamics

In J.D. Jackson's first chapter, he says the proper equation connecting $\textbf E$ and $\textbf D$ $$ D_\alpha = \sum_\beta \int d^3x'\int dt' \epsilon_{\alpha\beta}(\textbf x',t')E_\beta(\textbf x ...
3
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1answer
85 views

Current, Current density

edit: Hi I'm trying to find the magnetic field generated by a time dependent oscillating current in the quasistatic case ($|z|,r <<c\omega$) where r is the perpendicular distance from the ...