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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For a straight circular wire, what is the relationship between the self inductance and frequency?

Due to the skin effect, the AC inductance of a straight wire will decrease as frequency increases. Is there any formula that can describe this relationship?
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2answers
68 views

Computational advantages of various notations for electromagnetism [closed]

Most undergraduate electromagnetism classes and textbooks use vector notation to describe Maxwell's equations. However, there are other notations like differential geometry and geometric calculus ...
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1answer
31 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 ...
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0answers
56 views

Dipole moment of a system with net charge

I want to calculate the dipole moment of an object that is not neutral. I know for neutral charges the dipole moment has a rather simple form: $$d = \sum q \cdot z$$ But suppose I have a charge of $+...
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1answer
135 views

Is magnetic field due to an electric current a relativistic effect?

I was reading a paper of the same name by Oleg D. Jefimenko; here is the concerned text: [...] relativistic force transformation equations demand the presence of an electric field when the ...
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2answers
58 views

Question about using Gauss' Law with a surface at infinity

While doing homework, I came across a situation where I tried to make this argument: For a finite distribution of charges, I know that the electric field drops off to zero at infinity. So therefore, ...
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1answer
63 views

How is the divergence of electric field related to the electric flux? [closed]

From the explanation of Maxwell's equations, I found, the flux of an electric field is mathematically represented by the by the divergence of the electric field.Then, how is the divergence of electric ...
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0answers
15 views

magnetic field due to current carrying coils

In the Helmholtz configuration, why is the magnetic field between the two coils uniform (I know the mathematical expression)? Can anyone please explain this physically? When the distance between the ...
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0answers
9 views

Behaviour of bubbles on the surface of a liquid [duplicate]

When you observe a group of very small bubbles on the surface of say, a cup of coffee, you can see that when the bubbles get close enough to the edge of the glass, the get attracted to it and ...
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1answer
28 views

Confusion about the total bound charge of a sphere placed in dielectric

There is a solved exercise in which a charged sphere of radium $r=a$ is inside a dielectric material. The surface bound charge and the volume bound charge are respectively: $$p_{sp}=\vec{P}\cdot \hat{...
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3answers
136 views

What changes in the electrons before and after a voltage drop?

It is easy to visualize gravitational potential energy as a function of the position of height, and a change in this potential is manifested in a change in height. Further, by the work-energy theorem ...
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1answer
77 views

Does Gauss's law not hold when there are charges outside of the Gaussian surface?

For example, if I have a gaussian surface and a negative charge somewhere outside that gaussian surface, there's going to be a non-zero electric flux. However, According to gauss's law, electric ...
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0answers
35 views

Basic Vector field question about notation [closed]

I am taking my first class in electrodynamics and the problem I am working on has a notation I have never seen before Consider a vector field of the form $V= f(x)y + g(y)x$ Is this essentially the ...
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0answers
28 views

Can I emit light from an inductor? [duplicate]

As I understand it, inductors create a magnetic field when current flows through them, and light is an electromagnetic radiation. So, is it possible for an inductor to generate magnetic waves of the ...
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2answers
65 views

Why can't a neutral object attract another neutral object because of electrostatic induction?

So a positive/negative charge can attract a neutral object by causing the negative/positive charges to move closer to the source. However, if you have a neutral object and another neutral object ...
3
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1answer
54 views

Conservation of Angular Momentum in Einstein - de Haas effect

I am not really sure why the law of conservation of angular momentum should hold true in the Einstein - de Haas effect. Consider the following excerpt about the phenomenon (taken from Magnetism in ...
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1answer
115 views

How Do Low Kinetic Energy and High Kinetic Energy Atoms Attraction differ?

Will atoms of 2 difrent energy levels electron and/or Kinetic attract more than 2 Atoms at he same energy level? Do 2 high energy level atoms attract more than 2 low energy atoms?
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1answer
46 views

What's wrong with using the 4-current to find the potential of a moving particle?

According to Feynman (Lectures on Physics, Vol. II, 21–6), the potential of a moving point charge is: $$\phi = \gamma \cdot \frac q {4\pi\epsilon_0} \cdot \frac 1 {\sqrt{ \gamma^2 \left( x-vt \...
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0answers
30 views

Relationship between magnetic force acted upon a diamagnetic substance and the magnetic field applied to it

I have a sample of bismuth that I have applied a measured B-field to through the use of a solenoid electromagnet. I've been trying to find a formula relating the B-field to the force that the bismuth ...
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0answers
31 views

Light reflecting off a sphere

Suppose light of momentum $-P\hat{\textbf{k}}$ is shone on a sphere. What is the momentum transferred onto the sphere? I think the transferred momentum upon reflection is given by $(2P\hat{\textbf{k}...
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5answers
300 views

Applying Newton's 3rd law in electromagnetic systems

From this diagram: What is the action force here, and what is the reaction force? From two references, the wire and the magnet? *Assume the magnet being an electromagnet(air core, basically a ...
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0answers
22 views

The frequency induced by the alternating current

Let set up the experiment as followed. A string is stretched at two ends. Two magnet poles N and S are placed under and above the string. Now we let an alternating current go through the string with ...
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1answer
82 views

About curious form of Maxwell's Equations for a monochromatic field [closed]

In a review paper of Whispering-gallery waves from A.N. Oraevsky, he writes the source-free monochromatic Maxwell's Equations as $\nabla\times E = ikH$ $\nabla\times H = -ikE$ and he defines $k = (\...
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0answers
65 views

Magnetic field of a permanent magnet - numerical calculation

I'd like to understand methods for calculating the magnetic field generated by a magnetized piece of material, e.g. a permanent magnet. I was wondering about the approach described here as it seems ...
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1answer
48 views

What methods are used to breakdown an EM wave into different frequencies? [closed]

What are the methods that are used to breakdown an EM wave into different frequencies?
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3answers
167 views

Does waving a magnet around create light?

If I wave around a bar magnet, the magnetic field in the space around it changes. Is this enough to go through the whole speed of light derivation implying that the motion creates an electromagnetic ...
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1answer
39 views

EM Wave equation and dispersion in a plasma

I am currently studying for qualifiers and I am really stuck on this one practice problem and I want to understand why I am having such a difficult time. The idea is that we have a plasma with free ...
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0answers
66 views

Response function in plasma

I am reading an article where authors investigate how a particular type of electrostatic waves propagates in a plasma. They start with the Poisson's equation in the next form: $$\nabla^2 \phi(r,\...
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2answers
43 views

Skin effect explained in terms of the flow of charges?

Can the skin effect for em waves incident on a conductor be explained by the movement of free charges within the conductor (given that they as $t\rightarrow \infty$, $\rho\rightarrow0$)? And if so how?...
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2answers
101 views

Direction of torque due to magnetic moment

I have a problem with determining the direction of torque due to magnetic moment on a current loop. Since the torque is defined as $$ \tau = p_m \times B $$ so I guess the direction of the torque ...
2
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0answers
57 views

Electric field due to a current carrying loop

I want to know how I can calculate the radiated electric field in the far zone of the loop. Knowing that the loop is in center at the origin of a x-y plane Knowing that the loop as a time-harmonic ...
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0answers
39 views

How to Create a Strong Electromagnetic Field?

For a project, I need to make a strong electromagnetic field, but it has to be light, small, but about 1-2 teslas strong. The attached image is a simple drawing shows the direction I need to generate ...
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0answers
75 views

Which of Landau's books are suited for undergraduates? [closed]

Seeing how well-received Landau's books are, I want to know if any of them are suited for undergraduates.
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1answer
202 views

Why does the skin effect cause current to flow at surface of a conductor?

I have read that due to the skin effect we only need to coat e.g. cables with a good conductor to make them effective. I understand that when a em wave is incident on a conductor it only propagates so ...
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1answer
99 views

Why can't magnetic flux be no longer defined for non-zero diameter wire?

This is a continuation of my previous question: This is the concerned quote form Purcell's Electricity and Magnetism's Electromagnetic Induction: You may think that one of the rings we considered ...
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1answer
49 views

Difference between flux of wire loop and wire in a uniform magnetic field

How come when a wire loop sweeps out an area in a uniform magnetic field and moves with constant velocity there is no induced current because there is no change in flux. However, when a straight wire ...
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0answers
72 views

Problem in computing self-induction for a wire with zero diameter

This is quoted form Edward Purcell's Electricity and Magnetism; it tells about the problem of computing magnetic flux during self-induction for a wire with zero-diameter: You may think that one of ...
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1answer
164 views

What happens if a current flows through a wire wrapped around a magnetised material?

A cylinder of radius $a$ has a uniform magnetisation along its axis, which results in zero bound volume current density and a bound surface current density $M\hat{\phi}$. A coil with $N$ turns and ...
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0answers
32 views

How useful would mass EM communication be in Space? [closed]

Considering a Science Fiction question, it occured to me that in "populated" space, with no atmosphere, you might expect to find more EM interference than on Earth. Basically, if you are outside of ...
4
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2answers
144 views

How can one meaningfully say that one field generates the other in an EM-wave?

This is a follow up question to: Do the electric and magnetic components of an electromagnetic wave really generate each other? Clearly there are nuances of how one states the "mutual induction" ...
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19 views

Increase Phase Velocity by Losing Power

I just read some words from the book Optical Waveguide Theory by Snyder, Allan W., p226. It says that However, although it is possible for the phase velocity of a mode to exceed the maximum speed ...
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2answers
118 views

Electric Field “at” the surface of a conductor

It has been pointed out to me that the Electric field exactly on the surface of the conductor is conventionally taken to be $E=\frac{\sigma}{2\epsilon_0}$; does this come from taking the midpoint of ...
1
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1answer
49 views

How does this approximation of the $B$-field of a charged rotating disk for $z\gg R$ make sense?

Consider a disk of radius $R$ rotating with angular velocity $\omega$ and with a surface charge density $\sigma$. I have shown that the magnetic field as a function of the distance along its axis (z) ...
3
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2answers
74 views

Curl of a simple magnetic field and resulting current distribution

I've been doing some thinking lately and here is my question: If one imagines that there is an auxiliary magnetic field $H$ whose spatial dependence is given by equation: $$H(x,y,z)=y\hat{i}$$ ...
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2answers
39 views

Why is flux linked between a bar magnet and a coil same as the flux due to bar magnet from radius of coil to infinity?

Why is flux linked between a bar magnet and a coil same as the flux due to bar magnet extending from radius of coil upto infinity? It has been stated without any reasoning in this video. at about 1 ...
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1answer
25 views

Force from a large conducting plate [closed]

How can I find the distance to a test-charge, hoovering below a conducting plate? Newtons laws applies. $$ $$ According to this information, I conclude that the force is equal zero. It is not moving....
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0answers
27 views

Looking for materials with specific magnetic properties

To begin with, I am not a native English speaker and have very limited knowledge regarding magnetism and want to apologize in advance for probable use of incorrect terms. In the picture, M ...
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2answers
127 views

Is there any way to justify or derive the form of the Lorentz force from relativity theory?

Lorentz force is in this form: $$\vec{F}=q[\vec{E}+\vec{u}\times\vec{B}]$$ As we know, it is Lorentz-invariant. Is there any way to justify or derive its form from relativity theory?
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1answer
433 views

Biot-Savart law from Ampère's with multivariate calculus

Let us assume the validity of Ampère's circuital law $$\oint_{\gamma}\mathbf{B}\cdot d\mathbf{x}=\mu_0 I_{\text{linked}}$$where $\mathbf{B}$ is the magnetic field, $\gamma$ a closed path linking the ...
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1answer
66 views

Solved Gauss' Law for $\vec{E}$ without boundary conditions?

Why can I solve for the electric field of a point charge Q at the origin without boundary conditions? $\nabla\cdot\vec{E}=\rho/\varepsilon_0 = \delta(\vec{r})/\varepsilon_0$ is a 1st order ...