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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3answers
171 views

Are magnetism and electricity the same thing? [closed]

I have read at certain place electricity and magnetism are the same thing, bit in reality we see both have different properties.
3
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0answers
59 views

What is the origin of the “polarization catastophe”?

According to the Clausius-Mossotti relation, $$ \frac{\epsilon_r - 1}{\epsilon_r + 2}=\frac{n\alpha}{3\epsilon_0} $$ So when $n\alpha = 3\epsilon_0$, the relative permittivity $\epsilon_r$ ...
0
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0answers
40 views

Maxwell Equation in dispersive media Griffiths

I am wondering where is the following equation (9.162) of Griffiths Electrodynamics 4e from? $$ \nabla^2\tilde{E} = \tilde{\epsilon}\mu_0{\partial^2\tilde{E}\over\partial t} \tag{9.162}$$ I know ...
0
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1answer
44 views

Why does the inductance of a coaxial cable not depend on the number $N$ of coils?

Suppose we have a long coaxial cable like in the following figure: I want to compute the self-inductance $L$ of the cable. As I understand, given a coil with $N$ closely winded turns, through which ...
1
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0answers
51 views

Does Lorentz force affect the magnetic field?

When a charged particle moves thru magnetic field, it is affected by Lorentz force. But does the magnetic field surrounding the particle experience a force opposite to the particles Lorentz force ? ...
0
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0answers
18 views

Is polarization a meaningful notion for an EM mode in a close cavity?

For a generic close cavity, I suspect that all the modes are non-degenerate? Therefore, in each mode, at each point, the E field has a definite direction, and consequently, it is meaningless to say a ...
0
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1answer
45 views

How can equipotential planes differ in potential in an uniform field?

I'm trying to solve an exercise that asks me the field strength of an uniform electric field where equipotential planes differ by $1\ \mathrm{V}$ and are $2.5\ \mathrm{cm}$ apart. First of all, I ...
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0answers
19 views

what is the difference between mictomagnetism and spin glass?

What is the difference between mictomagnetism and spin glasses? I mean what are the distinguishing characteristics of them which makes them separate?
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0answers
34 views

How does the “computer fan with magnets” generator “work”? [duplicate]

This question is in relation to the following YouTube video: https://www.youtube.com/watch?v=jiAhiu6UqXQ In it, an electrical generator is shown consisting of a CPU fan with thin magnets attached to ...
0
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1answer
29 views

Induced current from moving coil through non-uniform magnetic field

A rectangular coil with dimensions $L_x$ and $W_y$ , mass $m$, $n$ turns , and resistance $R$ is moving at an initial velocity of $v_i$ when a non-uniform magnetic field pointing directly up ...
2
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1answer
26 views

What about a material makes it diamagnetic

For a material to be magnetic, all the magnetic atoms (atoms with half filled electron shells) need to be aligned, but what about a material gives it the property of diamagnetism?
0
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0answers
19 views

Can a material be diamagnetic to electromagnetic waves, such as the visible spectrum

Diamagnetism is shown to repel a magnetic field and therefore the material counterpart of that field. Can an object be diamagnetic to electromagnetic waves, and repel them? I understand that there is ...
2
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2answers
42 views

Is the photon truly not absorbed in Raman scattering?

In reading about Raman Scattering, I was thinking while reading it "okay, incident photo absorbed by molecule, molecule goes to higher energy vibrational state, molecule re-emits photon with either ...
1
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1answer
56 views

Why can't I measure electric potential from source to point according to this formula

The formula for electric potential of points A and B in the presence of an electric field due to a point charge where $R_a$ and $R_b$ are the distances from source to point A and B respectively is: ...
0
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1answer
51 views

If EM waves are made of oscillating electric and magnetic fields, how come photons have no charge?

I just recently learned that electromagnetic waves are made of oscillating electric and magnetic fields, and I have a question. In the standard model, photons are described as having zero charge, and ...
2
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1answer
31 views

Is this a standing or moving wave?

The electric field of a uniform plane wave traveling in a source free region of free space is given by: $ \vec E= (0.5j \vec x + \vec y)(e^{j \beta z} - e^{-j \beta z})$. Is this a traveling wave or ...
1
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1answer
36 views

Is the magnetic field calculated by Ampere's Law only because of the currents crossing the loop? [duplicate]

In Ampere's Law, $$\oint \vec B \cdot \mathrm d \vec l = \mu I$$ the current outside the curve is not included on the right hand side of the equation.* Does it mean that the magnetic ...
0
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0answers
48 views

What will be the motion of an electron kept at rest in the vicinity of a magnetic monopole?

Consider that both an electron and a magnetic monopole are kept at rest close to each other. Will this result any motion of the electron? If yes, please give a derivation of the equation of motion.
2
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2answers
79 views

Relation between magnetic moment and angular momentum — classic theory

How do I prove the relation between the vectors of magnetic moment $\vec\mu$ and angular momentum $\vec L$, $$\vec\mu=\gamma\vec L$$ ? Many text books and lecture notes about the principles of ...
1
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1answer
63 views

Two objects with mass m with charge q connected to spring [closed]

I am taking Physics 201 on Yale Open Courses. I having trouble with the 5th problem in the problem set 1, which says as follows: Two sphere of mass m and negligible size are connected to two ...
1
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1answer
72 views

Propagating higher order Hermite Gaussian modes. What are complex amplitude coefficients?

I've been tasked with writing a code (in MatLab, but I'm currently using Mathematica because I don't know MatLab %\ ...) to simulate the propagation of a Gaussian beam. I don't really know anything ...
2
votes
1answer
52 views

Force on permanent magnet solenoid core

I was wondering, since a coil/solenoid will pull any ferromagnetic material inside it, does the initial magnetization of the object in question affect the magnitude or direction of the force? I know ...
3
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2answers
103 views

Atomic explanation of magnetic field [duplicate]

We all know how an electric current causes magnetic fields. But when a single electron is flowing through the wire, how is this electron creating the magnetic field or how are electrons responsible ...
2
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1answer
45 views

How would an atom behave (in terms of atomic particles) if the electrons were much heavier than the nucleus?

In other words, does the mass of electrically charged particles affect the electromagnetic forces that operate between them ? Is the electrons revolving around the nucleus simply a consequence of the ...
1
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0answers
47 views

Electromagnetism and magnetic fields

Would it be possible to fill hollow non-magnetic blocks of metal with ferromagnetic fluids and use magnetic fields to move the blocks in a certain way? I am only asking this because I think that if it ...
0
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1answer
69 views

What is the magnetic flux density “outside” the solenoid when AC current is passing through it?

I know that there are well defined equations explaining the magnetic flux density in the solenoid. However what about magnetic field outside the solenoid? How is the magnetic flux density related ...
0
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1answer
31 views

Magnetic flux from an infinit wire through a Square loop [closed]

Okay so I need to solve this exercise. I know that the magnitic field from an infinit wire is given by: $ \vec{B} = \frac{\mu_0I}{2\pi r} \hat{\phi}$, And that I must do an intergral looking ...
0
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3answers
82 views

In the electric field we have dielectrics.What about the magnetic field?

Do we have insulators in the magnetic field just like we have dielectrics in the electric field? How are they called and how do they work?
0
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0answers
37 views

How to apply voltage source in FEM when solve Maxwell equation?

I need to solve the Maxwell equation of electric field by finite element method. In this function, the right hand side is the current density. However, in my problem, the voltage source with 1 MHz ...
1
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1answer
32 views

Correlation between entangled photon polarisation measurement?

From Malus's law we know that if we measure a the polarisation of light with a filter angle $\theta$ to the direction of polarisation then the intensity goes like: $$I=I_0 \cos^2(\theta/2)$$ Firstly ...
1
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1answer
42 views

Ampere's Law and Gauss's Law for EXACT CENTER of Finite Wire: Mathematical Justification [closed]

I have always seen it explained that: Ampere's Law (in integral form) works whenever B is constant around a path, so that you can pull it out of the integral. Similarly, if you can draw a ...
2
votes
1answer
28 views

Is it safe and theorotically correct to heat a bar magnet using an open fire/furnace, provided conditions given below?

For a project, I will have to heat a bar magnet to any temperature above 40 degree celsius. For this, can I place the magnet over an open fire --like one in a furnace-- for 20 minutes or so to achieve ...
0
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0answers
52 views

Is Jefimenko's assertion regarding E and B fields a physical fact? [duplicate]

Standard textbooks says: "Time varying Electric field and magnetic field produce each other". But Oleg Jefimenko says NO to this. Who is correct: standard textbooks OR Jefimenko ? Both can not be ...
0
votes
1answer
35 views

Why does a good conductor shows pronounced skin effect?

I am currently studying transmission of em waves and skin effect is puzzling me. Let us consider an em wave propogating in z-direction with electric field in x-direction & magnetic field in ...
3
votes
3answers
103 views

How does radiation degrade mechanical parts and electronic devices?

I'm running out of places to look (lots of Googling, SE, [articles and books are too specific and never give a good overview]), and yet I am still unsure about how exactly radiation can degrade ...
1
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1answer
49 views

How does one calculate or even approximate the force observed by a magnet as its dropped inside of a diamagnetic cylinder?

How does one calculate or even approximate the force observed by a magnet as its dropped inside of a diamagnetic cylinder? Wikipedia and Google does not provide much information on this topic. ...
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2answers
41 views

frictional force is nonconservative force [duplicate]

In nature there are mainly four kind of fundamental forces,electromagnetic force is one of them which is conservative force.If friction force is belongs to electromagnetic force then why it is not ...
1
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1answer
33 views

What do we mean by this statement : “some positive charge is put on a metal piece”?

What do we mean by this statement : "some positive charge is put on a metal piece" ? (I know it will be distributed on the surface of the metal piece, if metal is isolated.) Electrons are ...
1
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0answers
27 views

What does it mean to perturb the electromagnetic energy with respect to a change in a Lorentz frame?

I am perturbing the energy of an electromagnetic field using \begin{align} \dfrac{\partial U}{\partial \zeta} = \dfrac{1}{\mu} \boldsymbol{H}\cdot \dfrac{\partial \boldsymbol{H}}{\partial \zeta} + ...
0
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1answer
58 views

Problem with the Ampere-Maxwell Law [closed]

We know that $$J=\sigma E$$ where $J=dI/dS$ is the current density, $\sigma$ the conductivity, and $E$ the electric field. So, if we put that into the Ampere-Maxwell law, then the law transforms ...
-2
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1answer
78 views

Are we working in the double slit argumentation with destructive interference arguments?

Stimulating water with two long straight bars one could produce linear waves. Having the right distance between the bars and the correct frequency of the steady system we get in the middle between the ...
1
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0answers
85 views

Divergence Theorem, mathematical approach to Gauss's Law?

Let $D$ be a compact region in $\mathbb{R}^3$ with a smooth boundary $S$. Assume $0 \in \text{Int}(D)$. If an electric charge of magnitude $q$ is placed at $0$, the resulting force field is ...
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1answer
45 views

Can Ampere's Circuital law be used on an infinite number of alternating Helmholtz coils?

I have the following surface current density $$ \bar{\sigma}_s = \hat{\phi} \sin(kz) |\bar{\sigma}_s| $$ to approximate an infinite number of alternating Helmholtz coils stacked along the z-axis with ...
1
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3answers
64 views

stationary electron in a time varying field

A moving electron in a stationary magnetic field will experience magnetic Lorentz force given by $q(\vec v\times\vec B)$. But will a stationary electron placed in a time varying magnetic field ...
1
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1answer
44 views

Total time derivative of magnetic vector potential A

I am looking at this document, which tries to establish the Lagrangian of the Lorentz force. Everything is fine, but I don't see why: $$\frac{dA_i}{dt}=\frac{\partial A_i}{\partial t}+\frac{\partial ...
0
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3answers
86 views

magnet moving in space

I know that a time varying magnetic field produces an electric field even in the absence of a conducting body, because thats how em waves work. But can you say the same for a space varying magnetic ...
1
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1answer
46 views

$B$ field around an infinite wire symmetry argument

Consider the infinity current carrying wire wire drawn below along with the three possible components of the magnetic field at a point a distance $r$ from the centre. I know how to use symmetry to ...
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2answers
75 views

Why does the Schwinger limit fail to predict the electron radius?

One might think that the minimum electron radius is given by the Schwinger limit, since, were it smaller, spontaneous radiative effects might begin to occur. This value is 3.3*10^-14 m, but we know ...
0
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0answers
28 views

Magneto Optical Kerr Effects

I have a few questions on MOKE setup. Firstly, why is calibration of the coils necessary? Is it to get a relationship between the voltage and the Magnetic field? Secondly, why do we have to normalise ...
3
votes
3answers
433 views

Why can't a magnet change a charged particle's speed?

I know that magnetic force acts perpendicular to the direction of the original velocity, so the velocity in that original direction is unchanged, but once the magnet starts acting, the particle's ...