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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Electro magnetic Wave? [duplicate]

I understand the fact that a static charge produces an electric field around it. I accept the fact(without questioning) that a moving charge produces a magnetic field. Question 1 : If a moving ...
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35 views

How exactly are the relative strengths of gravity and electromagnetism quantified? [duplicate]

I've often heard it said that gravity is much weaker than electromagnetism, and after looking at several questions on SE, I feel that I've got at least a qualitative handle on the concept -- gravity ...
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2answers
40 views

How does calblock (water softener) work?

This "calblock" device claims to prevent limescale accumulation on water heaters in a washing machine. It sits between the water faucet and the washing machine; the water passes through it. I cannot ...
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1answer
19 views

A doubt on Magnetic domains and electron orbits

If electrons spin not in 2d orbits but 3d orbitals, how is it that in the magnetic domain explanation, we say that electron's motion around the nucleus is like a current loop and hence we get the ...
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32 views

Polarization in high energy vacuum non-linearity?

I heard that the vacuum becomes nonlinear at high energies. What is an intuitive explanation as to why this happens? For example, in classical optics non-linearitiy comes from material field ...
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1answer
56 views

Why does a toroidal coil transformer work - it should not! [closed]

A time variant current through a coil wound around a toroid core will produce a time variant magnetic field within the volume of the toroid, but no field external to that volume. Since a time variant ...
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36 views

Is polarization a stable state?

Do a polarized light beam stays polarized over large distance or does it kind of relax and eventually become unpolarized?
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36 views

Scattering electromagnetic waves [closed]

I have a question about "Rayleigh Scattering efficiency", can you give me equations that describe it?
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20 views

Is the electric field inside a conductor always zero? [duplicate]

We just learned in physics that a field inside a conductor is zero. My question is, is this always true? For example, what about if you were inside a hollow iron sphere 10 feet from a hugely ...
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1answer
50 views

What is the complex dipole moment?

I have some problems with getting the complex (time dependent) dipole moments of some dipoles in a configuration. I eventually want to get the electric and magnetic fields of the configuration, but my ...
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25 views

Direction of induced current

Find the direction and Magnitude of Induced Current and Induced Emf if the magnetic field is inside the screen $B$ and starts diminishing. The Resistance of each wire is $R$. I am confused, how to ...
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22 views

magnetostatics and time varying fields

Mathematical statement for magnetostatics is $\nabla\cdot \mathbf{J}=0$ which accounts for no piling of charge and hence no time varying field term in the 4th Maxwell's equation.Are there any possible ...
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12 views

does thickness of a diamagnetic material affect the mag-lev effect?

I built a little mag-lev display, basically a desk ornament, as a fun project/learning experiment. It's a fairly basic setup with a neodymium magnet suspended between two thin sheets of pyrolytic ...
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38 views

How does the temperature of a magnet affect its characteristics? [closed]

How does the temperature of a magnet affect its characteristics? Is a hot or cold magnet stronger? Or does it not matter?
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81 views

Why do we need to add $\frac{r'}{c}\frac{d}{dt}\left(\frac{\bf e_{r'}}{r'^2}\right)$ to retarded Coulomb field in retarded electric field's formula?

The retarded electric field is given by: $$\mathbf E= \frac{q}{4\pi\epsilon_0}\left[\frac{e_{r'}}{r'^2} + \frac{r'}{c}\frac{d}{dt} \left(\frac{\mathbf e_{r'}}{r'^2}\right) + ...
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1answer
110 views

Ampère's law from Biot-Savart law for linear currents with multivariate calculus

My book, W.E. Gettys's Physics, starts from the Biot-Savart law $d\mathbf{B}=\frac{\mu_0}{4\pi}\frac{Id\boldsymbol{\ell}\times\hat{\mathbf{r}}}{r^2}$, ...
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14 views

The magnetic fields [closed]

what is the origin of magnetic field in terms of spin and angular momentum of a charged particle?can spin produce magnetic field? the magnetic field is produced by moving charges. I think i mix the ...
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0answers
21 views

DIY ultrasonic cleaner - will it work? [closed]

I want to build some simple ultrasonic cleaner and I wonder: is my idea going to work? The plan is: Build a container from metal sheets or just find/buy some container. Buy something like 60W 40 kHz ...
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0answers
52 views

What's the analogy of a single photon from the perspective of “classical electromagnetic wave”?

I guess there isn't an accurate analogy. But what is the best analogy we can use? It seems an idea sinusoidal wave of a single frequency doesn't fit as a photon at all. In a certain sense, at least ...
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83 views

Distribution of surface charges in an electric circuit

I'm reading Sherwood and Chabay's brilliant textbook Matter and Interactions, in particular the section that deals with how the surface charges in an electric circuit distribute themselves to generate ...
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0answers
26 views

Calculating torque needed to climb a graded hill [closed]

this is my first post but I'll try to give my best understanding of the problem. I've been designing an electric skateboard which is driven by only one of the rear wheels (for the moment). As I was ...
3
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0answers
37 views

Lorentz force on superconductors?

If current flows on the surface of a superconductor(for both type I & II) and is exposed to an exterior magnetic field, will a superconductor experience a Lorentz force? Knowing that a ...
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14 views

Would a previously poled piezoelectric material experience a force aligning it with an external electric field?

I'm wondering if it would possible to crush a poled PZT object, disperse the powder into a thermoplastic (with a melt temperature below the Curie temperature of PZT) and align the 'crystal shards' ...
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40 views

emf of a moving wire in a variable magnetic field

Lets, say that Magnetic filed is either (case 1) $B=B_0$ or (case 2) $B=B_0\sin{\frac{\pi x}{L}}$in $z$ direction. We have a wire with a length of $L$ along $y$ axis which is moving in $x$ direction ...
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3answers
89 views

If we consider the electric field to act upon charges with a force, how does it stay in line with Newton's laws?

This should be a relatively simple question. Let's say we have a constant electric field $\textbf{E}$ in a conductor. The electric current density would then be $$\textbf{j}=\rho \textbf{v}$$ where ...
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1answer
48 views

Electric field of a moving charge with Lorentz transormation

I was going through this link http://physics.weber.edu/schroeder/mrr/MRRtalk.html There it says Now consider the electrostatic field of a point charge at rest, shown at left below. At every ...
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27 views

Capacitor connected across two isolated sources [duplicate]

Lets say there are two isolated sources of positive charges $q_1$ and $q_2$ $(q_1>q_2)$ located sufficiently far apart. If the two are connected to the two plates of a capacitor, then what is the ...
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90 views

Why is there no induced current in this loop? [closed]

This problem comes from Barron's SAT Subject Test Physics book. A loop of wire and a bar magnet are moving relative to one another. Which motion in the diagrams shown below will NOT induce a ...
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21 views

Concentration and manipulation of magnetic fields [duplicate]

is it possible to concentrate magnetic fields, via concave electric coils? If a current is induced in such as a concave cylinder shaped coil.
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180 views

Why does electromagnetism have torsion, whereas gravity does not?

Why don't we use torsion-free covariant derivatives for QM, even though we already do so in the case of GR? In general relativity, we use the Levi-civita connection, a torsion-free connection ...
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44 views

What is capacitance, in general?

In circuit analysis software capacitance can be measured between any two nodes of a circuit or of a multiterminal device. In practical terms we take $C_{ij}$, the capacitance between $i$ and $j$ as ...
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45 views

Why is one Telsa equal one weber per square meter instead of one weber per cube meter?

Lines of magnetic flux exist in three-dimensions, so how can they be measured per area unit?
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52 views

Magnetic field existence - a relativistic approach

Recently I learnt that magnetic force is equal to relativistic electrostatic force. With this approach I was able to understand the motion of a charged particle kept near a current carrying conductor. ...
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74 views

Are the conducting electrons in a metal counted as free or bound charges?

Caused by another question on the propagation of EM waves in a metal, I got a bit confused on the notion of free and bound charges in a metal (sometimes called induced or external). Are the free ...
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11 views

How polarized object's polarized atoms behaves like charge?

Electrical polarization is just the shifting of the constituent atoms' protons and electrons in opposite directions. This creates a bound charge, and this bound charge creates voltage and thus an ...
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1answer
58 views

By what mechanism is a photon emitted or absorbed in atomic electron state transitions?

I understand atomic emission and absorption spectra well - photons of a specific energy can be emitted or absorbed by atoms, if that energy corresponds perfectly to the energy difference between two ...
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1answer
22 views

Generation of back emf with relativistic approach to EM Waves

I learnt that Magnetic force around a current carrying conductor is nothing but relativistic electrostatic force observed by a charge particle from its frame of reference. But I am not able to ...
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78 views

Dispersion of light in metals and the plasma frequency

I've been reading about the dielectric function and plasma oscillations recently and I encountered the following dispersion relation for EM waves in metals or in plasma (Is it correct to treat those ...
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31 views

Screening of electrostatic potential at the interface between two dielectrics

The motivation of my question: Calculating the dispersion relation of plasmons in a graphene layer embedded between two dielectrics with different dielectric constants. Addressing my question: I ...
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38 views

Plane wave interaction with dielectric slab

Can anyone help me with this classical EM / optics problem? A plane wave is incident on a rectangular slab of a dielectric material. What is the form of the field in the region beyond the slab? ...
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1answer
31 views

Factors affecting magnitude of induced emf in coil

Does the magnitude of emf induced in a coil depend only on the rate of change of flux? Does it depend also on the amount of flux linked to it? Will the change of flux from $50 ~H$ to $40 ~H$ and ...
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1answer
19 views

How do you calculate the back emf?

I am trying to compute the back emf in a solenoid of radius $a$, with length $l$ and $N_1$ turns and a driving current $$I(t)=I_1\cos(\omega t).$$ I thought it would be a good idea to begin by ...
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1answer
15 views

Hysteresis curve for ferromagnet different types?

If you type 'hysteresis curve for ferromagnetic' in to google you get several different types. Looking at the once with $B$ against $H$ there are some that appear to go flat at satruation: And ...
3
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1answer
43 views

Description of transparency of a Faraday cage to different frequencies?

A Faraday cage within a static electric field leaves an internal electric field equal to $\vec{0}$ (as long as there are enough mobile electrons in the conductor to counteract the external $\vec{E}$). ...
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1answer
44 views

How much time for a magnetic field to disappear?

Consider current flowing through a conductor. When I disconnect the power to the conductor there should be a surge in the magnetic field the moment the current touches zero. My question is how long ...
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2answers
34 views

Using electromagnets to hover a craft independently of the surface below it

Why isn't this possible? I've seen the ducted fans, it works (even if it is very rough). I've also seen the magnetic boards that hover above a special magnetic-reactive surface. But that isn't true ...
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25 views

How do magnets break rotational symmetry?

I have heard that magnets break rotational symmetry, but I do not understand why? In context, I believe they are talking about the local magnetization vector in the material when they say a magnet ...
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1answer
62 views

Magnetic field felt by an observer “orbiting” a proton

Classically, if one has an electron orbiting a proton, how can the magnetic field felt by an observer with the same instantaneous velocity as the electron be calculated? It seems that I may find the ...
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1answer
131 views

Fusion, Magnets and Quantum Generators [closed]

I cannot even play like I'm even at this level, but this is the fusion reactor in Germany called the Wendelstein 7-X stellarator. These doughnut-shaped magnets (often seen on Physic Exchange) are ...
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79 views

Mathematics of Surface Divergence and Surface Curl

While studying electrodynamics I found two functions - Surface Divergence and Surface Curl - that seem to condense the formulas for superficial discontinuities of the electric and magnetic fields ...