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.

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36 views

Induced EMF dependent on terminal wire connection?

Figure(a): When a conductor moving inside magnetic field, of a given length at a certain velocity the induced EMF is: $$\epsilon = vBL$$ However, what if we changed the position where the bottom ...
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24 views

Electric dipole moment of a coaxial cable?

Question Does a cylindrical coaxial cable have a net electric dipole moment, and if so why? Context I am trying to understand why the heart has a net electric dipole moment. In the heart we have ...
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64 views

how tight winding of coils in solenoid reduces external magnetic field?

My book says that the tendency to have zero field outside and a uniform field inside become more and more effective as the solenoid is more and more tightly wound.Can someone justify this statement. I ...
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1answer
98 views

Relativistic explanation of Radiation

I ask this question again in a simpler, shorter form. Maxwell's equations can be derived with Special relativity starting from the Coulomb's law. Therefore all the phenomena of classical ...
3
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1answer
158 views

How is Biot-Savart law verification of Maxwell's 4th equation for steady current?

Please provide some theoretical procedure which equates Biot-Savart law with the Maxwell's 4th equation for steady current, which is Ampere's law $$\quad \nabla\times{\bf B} = \mu_0{\bf J}.$$
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12 views

Analysis of diagonal Lorentz force & Induced EMF of this orientated wire

Given this diagram: A conductor of a certain length $L$ placed in a magnetic field $B$, has the terminals connected to the top&bottom edges of the conductor. Current(even though scalar) would ...
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18 views

Is there theoretical description of such plasmonic nanostructure?

I'm preparing a reasearch about plasmonic nanoparticles and I'm interested about their arrays placed above a metallic film (like on the picture). Until now i found following articles: ...
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1answer
88 views

Energy of a permanent magnet railgun

I'm creating a permanent magnet railgun, which essentially uses two conducting rods with a row of magnets between them and a conducting projectile laying across the two rods. I am trying to determine ...
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0answers
24 views

Center of Lorentz Field

I am currently trying to write a particle physics library and I have implemented gravitational, spring, and Lorentz interactions between particles. These implementations can be seen here if desired. ...
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1answer
38 views

How to collimate the LASER light using an electric field? [closed]

The He-Ne laser beam is passed through electric field plates. What is the mechanism occururing there and the principle of LASER light interacting with electric field?
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1answer
49 views

Auxiliary magnetic field identically zero?

Consider a 3D space that's filled up completely with a material of fixed magnetization $\mathbf{M}$ (i.e. everywhere in space the magnetization points in the same direction and has the same ...
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0answers
76 views

Magnetic monopole using differential forms

I'm trying to understand the different variations of the Maxwell's equations using differential forms. The Maxwell's equations are $$dF=0\\ *d*F=J$$ where $F$ is the electromagnetic tensor ($F=dA$) ...
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1answer
40 views

How is an electron beam generated?

I am trying to get a better handle on how the EBPVD machine works in the lab I am working in. I understand that it produces an electron beam with a tungsten filament and that beam is then directed ...
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64 views

The Inertial theory of Sciama and an electromagnetic analogue

In 1952 D. W. Sciama introduced a paper On the origin of inertia. It presents a method in which inertia could arise from other mass in the universe. It goes along these lines: If you try to ...
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31 views

Magnetic field of a circular loop if r<R

Given a circular loop of radius R and is on the xy plane with the center at the origin. Let P=(λR,0,0) be a point on the x-axis such that λ<1. Find the vector potential A at P as a power series of ...
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0answers
26 views

Does current understanding of EM theory provide any evidence of additional physical dimensions?

Some theories (such as variants of the String Theory) postulate the existence of additional dimensions beyond the 3 spatial dimensions. So I was thinking that if such dimensions exist, perhaps some ...
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3answers
80 views

Light interference with light and other EM waves [duplicate]

Lets assume a room with one or two sources of light (normal light bulbs or fluorescent lamps). So if we look at lamp from any direction we see it. We also see different objects in the room because of ...
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1answer
46 views

Why are waveguide fields not infinite?

I was reading The Feynman Lectures on Physics, Volume II, when I got to the section on waveguides. Toward the end, Feynman uses the concept of an infinite number of alternating line sources to explain ...
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1answer
49 views

How to find the magnitude of electric and magnetic fields in an arbitary inertial frame?

In the context of special relativity, and using proper Lorentz transformations: If the electromagnetic fields have an uniform value [= constant in space and time] in an inertial frame, how will the ...
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1answer
31 views

Induced EMF in our body

I have learnt today that, Faraday And Henry independently found that In the changing magnetic flux, there will be Electric current in the conductor. Then why our body don't feel shock when we move ...
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2answers
4k views

Can sugar be affected by a magnetic field?

While I was making a morning coffee at work, some sugar from the spoon started to fly away, seemingly towards some foam cups. Can this be explained by magnetism?
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10 views

Magnetization in a “fixed-ratio” (or “hard”) transformer

I've done a simple experiment related to 2 types of transformers: isolated transformer (regular transformer) and "fixed-ratio" (or "hard") transformer. For the former in which the primary and ...
1
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1answer
68 views

Dipole antenna $E$-field direction

I was looking up dipole antennas on Wikipedia, among other sites. I came across this animation: and was wondering why there wasn't any field lines in perfectly vertical direction. In the case of a ...
1
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1answer
88 views

What form of energy is magnetism stored in?

In physics class I was told that there are 9 forms of energy: -Electrical -Light -Thermal -Nuclear -Elastic Potential -Gravitational Potential -Sound -Kinetic -Chemical So, my question is, ...
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3answers
76 views

How can one produce a projected electric field? [closed]

Original question: How can one produce an electric field? I understand that there is a method involving metal sheets and running an electrical current through the parallel sheets. However, is there a ...
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2answers
65 views

Magnetic field at the center and ends of a long solenoid [closed]

A long solenoid has current $I$ flowing through it, also denote $N$ as the turns per unit length. Take its axis to be the $z$-axis, by symmetry the only component of the magnetic field inside is ...
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4answers
262 views

Path of EM wave propagation in a circuit wire

The image is my visualization of drift velocity and electromagnetic (EM) propagation of charge wave in a closed circuit. The slow drift velocity of the electrons follows the path of the circuit (a ...
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177 views

Interpretation of QED gauge freedom

In quantum (or classical) electrodynamics we are free to make gauge transformations, which change the form of terms in the Feynman diagrams (or the potentials) without affecting any physical ...
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2answers
286 views

why don't large magents repel themselves

This question may have been asked before so I apologize in advance if it has. I've been playing with some magnetic buckyballs I got recently (highly recommend getting some if you dont have any) and ...
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0answers
24 views

Vector potential $ \vec A$ of two parallel conductors

Let's say we have two parallel conductors of length $l$ parallel to the x-axis at $y=y_0$ and $y=-y_0$. Let's say the upper conductor has the current density $j$ and the lower one $-j$. Now I want ...
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0answers
20 views

Precession of a charged rotating sphere

Can anyone explain to me the second part of this question?
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2answers
73 views

Can an electric field be there without a charged partical?

How does a photon have an electric field around itself without any charge particle inside it.
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2answers
53 views

Do a receiving antenna interfers with an emitting antenna?

As I understand: Accelerating electrons generate electromagnetic waves. An emitting antenna have an alternating current (electrons are moving) which generates an electromagnetic waves. The ...
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0answers
35 views

Given magnetic field, calculate electric field

The B field depends on z and t so that $B = j B_{0}cos(kz-\omega t)$ where k is the wavenumber, $\omega$ is angular frequency and $B_{0}$ is constant. The electric field is $E = E_{x}i + E_{y}j ...
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0answers
25 views

magnetic field and permeability

Doubt on magnetism. The the problem with Magnetic Flux Density($B$) and Magnetic field intensity($H$). I can Imagine magnetic flux($\Phi$) lines and flux density($B$) Physically. But magnetic field ...
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1answer
176 views

What is wavelength of electric field generated in a wire? [closed]

I read link given below: http://en.wikipedia.org/wiki/Speed_of_electricity Above link says _The speed at which energy or signals travel down a cable is actually the speed of the electromagnetic ...
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19 views

Does inductors oppose the same change in current that it itself produces in case of DC Current?

We know that the inductor is a solenoid. In that solenoid, due to self induction it produces its own emf. That causes a change in the initial current. To counter this change the inductor produces ...
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1answer
59 views

Self induction in a circular coil

There's a formula for self inductance : $$ L=\frac{n\Phi}{i}$$ where n is the number of loops. But the book also says self inductance is directly proportional to $ n^2 $ I totally agree with the ...
2
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0answers
35 views

Meaning of components of Maxwell's stress tensor $T_{ij}$

I am learning about Maxwell's stress tensor and what I understood is that the components, say $T_{ij}$ is something like a force parallel to the $j$th-direction acting on the surface with its normal ...
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0answers
19 views

Are magnets attracted to mu-metal?

Are magnets attracted to mu-metal? Be aware that when watching videos of mu-metal they may have metals that are attached to the mu-metal and are attacted to magnets. Please don't get them confused.
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1answer
49 views

Retarded potentials and fields

Why can't we use retarded times to make an expression for retarded fields instead of potentials? As far as I know it doesn't work, since the solutions produced ("retarded fields") don't satisfy ...
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1answer
42 views

How does current increase in an LR circuit in order to reach a steady-state?

The equation of voltage of an LR circuit is given by: $$\boldsymbol{\varepsilon_0} - L\frac{dI}{dt}= RI\;.$$ Now, before the circuit is closed, $i= 0\;$ As is written in books, the current then ...
2
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1answer
47 views

Time dependent electric field: Mathematical expansion for local electric field

In many articles and books I see that local electric field is expanded as $$\vec E_0(\vec r(t)) = \vec E_0(\vec R_0) − (\vec a(t) \cdot \nabla) \vec E_0(\vec R_0) \cos(\Omega t) + \ldots $$ For ...
3
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4answers
222 views

Interesting problem involving pendulum, collisions, and electric charges

This problem was invented by the physics professor at the community college near me which he used on a past final exam: A pendulum consists of a massless rod of length L and a conducting ball of mass ...
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1answer
23 views

Why does emf of a cell equal to $\frac{F_b d}{q}\;?$

In Concepts of Physics by H.C.Verma, it is written: Some internal mechanism exerts forces on the charges of the battery material. ... We show the force on a positive charge $q$ as $\vec F_b\; .$ ...
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2answers
82 views

Why can the divergence of vector potential be anything?

Purcell in his book was deriving the vector potential $\bf A$ using $\text{curl}\;(\text{curl}\; \mathbf A)= \mu_0 \mathbf J\; .$ After some algebra, he came to this: $$-\frac{\partial^2 ...
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1answer
63 views

Is there a way to write the Lorentz force in terms of one field, $L$, and one charge, $X$?

I have heard that physicists like to write electromagnetism as one force (the Lorentz force) and define it as $\vec{F_L}\left(q, \vec{v}, \vec{E}, \vec{B}\right) = q\left(\vec{E} + \vec{v} \times ...
2
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0answers
24 views

Why are only some materials ferromagnetic? [duplicate]

I've been told in my solid state class, that ferromagnetism occurs when electron spins are alligned. This happens, as I understand it, when it is "energitically favorable" and when the wavefunction is ...
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4answers
139 views

Why does the frequency of a Transformer not change?

I was reading about the transformer, when I came across a note by the author that stated that the Frequency is not changed as the flux linked to the secondary coil in a transformer changes. Is there ...