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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Intrinsic and normal B-H curves in magnets

In a magnet, what is the difference between the intrinsic $B-H$ demagnetization curve going from $B_r$ to $H_C$ (which has a knee) and the normal $B-H$ curve going from $B_r$ to $H_{ci}$ (which is ...
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1answer
55 views

what is the physical significance of dielectric constant and loss tangent?

I want to know that the significance of dielectric constant and loss tangent behaviour. How it characterises the materials. and possible relation between the dielectric constant and polarisation ?
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1answer
47 views

Would moving quarks constitute a current?

I know that it would take an almost infinite amount of energy to isolate quarks, but let's say we've gotten past that and we have isolated quarks and put them in motion. Would that be a current since ...
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27 views

Double Fraunhofer , Fourier transform to the image plane?

Consider the diagram below: I know that from Franhofer diffraction we have: $$u_f(x_f)\propto \int u_o(x_o) e^{-k\frac{x_f}{f}x_o} dx_o$$ Assuming small angles. I also know that $u_i(x_i)$ is ...
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2answers
173 views

According to relativity theory, what is the force that two electrons moving radially apart exert on each other?

According to relativity theory, what is the most general expression for the force that two electrons moving radially apart exert on each other? I am looking for a function $$F(r(t)),$$ where $F$ is ...
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1answer
45 views

Problem with magnetic field due to relative motion

We know that, moving charge produces magnetic field in the surrounding space. Consider this scenario : A charge 'q' is moving with a constant speed 'v' in the direction of positive x axis of a ...
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26 views

Scanning Electron Microscopy on a smaller scale

Is it possible to sufficiently focus a ~1nm beam of electrons into a sample chamber in less than 10cm of vertical space, therefore reducing the volume of the entire vacuum chamber, and subsequently ...
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2answers
102 views

Why doesn't sunlight ALWAYS get split (into monochromatic) when going through the clouds?

It is my understanding that clouds are largely made up of water, which is known to split white light into its frequency components, and that's why we see rainbows sometimes. My question is, with ...
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0answers
44 views

Mass term in Maxwell's Lagragian for Electromagnetism

In the scalar field Lagrangian the mass term is given by $$m^2 \phi^2.$$ But the equivalent term in Maxwell's Lagrangian for electromagnetism is $$m^2A_{\mu}A^{\mu}.$$ But I don't know why the ...
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1answer
46 views

Electromagnetic waves of accelerating charges

Is it true that more accelerating a charge will cause electromagnetic waves of more energy than the energy of the electromagnetic waves cause by lesser accelerated charge ?
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2answers
49 views

northern hemisphere compass points where in southern hemisphere?

If Northern Hemisphere compass points to magnetic north and this same compass is brought to the Southern Hemisphere, will the 'painted red north' compass needle be drawn to the magnetic south pole?
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1answer
39 views

Amplitude of electromagnetic wave

For an EM wave propagating in +z direction, it is described by $ \underline{E} = \underline{E_0}(x, y)e^{i(kz - wt)}$ I know that the imaginary term in the expression describes phase and $|\...
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21 views

Constant scalar magnetic potential in ferrofluid

I have read in an article that a ferrofluid with very large magnetic permeability (I gess it means that the magnetization of the fluid is the saturation magnetization) under a constant external ...
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0answers
30 views

Charge that moves inside a conducting sphere

I have a conducting sphere of charge Q and inside it we set a charge -q from the centre with initial velocity uo and i would like to know with what speed it reaches the surface of the sphere and what ...
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0answers
15 views

Sources for the magnetic exchange integral in group d transition metals

Does anyone know where I can find values for the magnetic exchange energy, J for elements with the atomic numbers 20-30? I've found values of 0.015meV, 0.03meV and 0.02meV for iron, cobalt and Nickel ...
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17 views

Boundary conditions while finding electric potential inside some specific volume

Please see the figure. Continuous charge distributions are in blue color. Inside cavity there is some charge distribution. Also On surfaces S1 and S2 there are some charge distributions (not shown)....
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2answers
125 views

Proton and electron joining

If I have a proton and an electron at rest at some distance apart. Will they form an hydrogen atom when released or they will join together? My intuition says it will form H atom. But I cannot ...
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0answers
32 views

Self propagating EM waves mechanism of propagation

Electric fields generate magnetic fields and visa/versa,and this is attributed to be how a light ray self propagates. Can anyone further clarify how exactly light rays self propagate? If the mechanism ...
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1answer
99 views

Lagrangian density for Lorentz force of continuous charge distribution in external field?

It's frequently an exercise to derive the Lorentz force law for a particle with charge $q$ in an external electromagnetic field given by the following Lagrangian: $$L = -mc^2\sqrt{1-\frac{\dot{r}^2}{...
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1answer
80 views

Magnetic monopoles in field theory

In standard QED, we couple the electron to electromagnetism by replacing $$\partial_\mu \to \partial_\mu + i e A_\mu.$$ Upon taking the classical limit, we find that this gives electrons an electric ...
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1answer
77 views

Force on a current carrying wire of arbitrary shape in a magnetic field

To obtain the net force by an external magnetic field on a current carrying wire, we divide the wire into small sections of infinitesimal lengths. The force due to the magnetic field on a given ...
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4answers
3k views

What is the explanation of the non-existence of magnetic monopoles? [closed]

Electric monopoles do exist, but why cannot magnetic monopoles exist? I know that magnets have two different poles, and when we cut them, both pieces will have again two different poles. But why does ...
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1answer
26 views

'Printing' magnetic polarity into a material

There is a company out there that 'prints' magnetic pixels, a.k.a. maxels, into a material. In doing so, they're able to choose the distance of effect of magnetic fields they create, independently of ...
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0answers
30 views

Can accelerated charged particle gain energy from charged medium? [closed]

Suppose a charged particle is moving in a medium. If it is accelerated, it is well known that it radiates energy (even in the vacuum). I was wondering if the charged particle would accelerate through ...
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3answers
87 views

when current passes through a wire , does it only travel through the outer surface?

In electrostatics we are taught that the field inside a conductor is always zero . So when current passes through a wire , the electricity only passes through the surface of the conductor . In ...
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1answer
39 views

differences of Aurora Borealis (North) vs. Aurora Australis (South)

I was wondering about the differences between the Northern vs. Southern lights: will one pole collect the positive charges, and the other the negatives? I know that the solar wind is composed mainly ...
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0answers
32 views

How can neutral conductive fluids create a magnetic field? [duplicate]

It's a standard textbook answer that currents of molten iron inside the Earth create the Earth's magnetic field. Matter, on the supermolecular scale, is electrically neutral. So any magnetic field ...
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31 views

How does the velocity of a magnet falling through a solenoid affect the induced voltage?

Given Faraday's Law, $\mathcal{E}=-N \frac{\partial \phi}{\partial t}$, we can induce an EMF by dropping a magnet through a coil of wire. How would the velocity of this magnet relate to the induced ...
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42 views

Deriving an equation in Maxwell's “a treatise on electricity and magnetism” [duplicate]

I am reading Maxwell's "a treatise on electricity and magnetism" and I need a derivation of formula 16 $\left(M=\iint\dfrac{\cos\varepsilon}{r}\mathrm ds~\mathrm ds'\right)$ (in the page below) using ...
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0answers
15 views

How to find the polarization (phase) of the virtual source if image theory is used

Consider a radiating element (actual source) is placed above a ground plane, and if we apply image theory to determine the E-filed, the virtual source will be placed below the ground plane and ground ...
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0answers
37 views

Magnetic field inside a solenoid

I'm trying to understand how to calculate the magnetic field inside a solenoid. However I don't understand why we choose to take a rectangular loop with one side inside the solenoid and we don't take ...
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1answer
38 views

Why does the primary coil get very warm with DC supply but not with ac supply?

It's about an investigation carried out on the transformer effect . The primary coil of 20 turns and the secondary coil of 50 turns is wound around a laminated iron core.
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1answer
47 views

Birefringent filter, optical path length difference?

In 'The Light Fantastic' by Kenyon, I.R. (p424), it is said that for a birefringent material inclined at Brewster's angle and who's optical axis lies in the plane of the plate, we have an optical path ...
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1answer
32 views

Verify Faraday's law of induction [closed]

I need to design a procedure for an experiment to verify Faraday's law of induction. I'm given: A Helmholtz coil of radius 15 cm Three plastic spheres of radii 1 cm, 1.5 cm, and 2 cm. A spool of ...
5
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3answers
108 views

Energy of an accelerated charge?

Thought experiment: Let's take a positively charged particle and place it in a vacuum with no electric field. It just sits there. Now, we instantaneously introduce an electric field. The moment ...
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0answers
34 views

Calculation of Phase Delay of a Curved Planar Dielectric Waveguide (i.e., bend)

I am working on a very phase sensitive planar dielectric waveguide device and I need to calculate the phase delay induced by a bend of some radius, $r$ and of $\phi$ radians for a give planar ...
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33 views

Effect of shielding on a miniature Helmholtz coil

So a bit of background... I'm a university graduate student with primarily digital signal processing and embedded experience. However I've managed to get myself involved with a project that requires ...
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1answer
27 views

Does the sign of imaginary part of complex permittivity have any physical meaning?

I have noticed some papers having written complex permittivity as $e' + je'' $ and others as $e' - je''$. The data in literature does not specify the sign. What should I use and does the sign of $e''$ ...
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2answers
58 views

Electric field around a moving charge

A moving charge has magnetic field around it. Is it just increased electric field in relativistic frame? If yes, does a moving charge has more electric field around it?
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1answer
86 views

Wave operator applied to electromagnetic field tensor

I'm trying to understand an argument in "An introduction to general relativity" by Hughston and Todd (p37). Let $F_{ab}$ be the electromagnetic field tensor, I'm trying to show: $$\Box F_{ab} = -4 \...
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23 views

Parallel wires in a changing non-uniform magnetic field?

Given this diagram: Where four copper wires are parallel to one another, connected to an exterior circuit(not shown) placed in a non-uniform magnetic field $B$ that is changing over time. Due to $...
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0answers
35 views

Amplifying an electromagnet's generated field

Given an electromagnet like this: which is essentially an iron casing with coils inside: Is it right that the centre disc would have one polarity whilst the outer housing another? To boost the ...
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0answers
8 views

Rotating magnetic field dencity

How to calculate the magnetic field density (Tesla) in a rotating magnetic field produced by 3 sets of coils at 120 degree angles.
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1answer
43 views

What happens when a magnet is dropped through a solenoid with a current running through it?

I know when a magnet is dropped through a copper tube or a copper solenoid it induces a current in the copper and the magnet actually slows down as it falls through the tube, but if I did this with a ...
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1answer
55 views

Are neutrinos affected by electromagnetic forces?

I know they don't interact with matter nor any electromagnetic forces, but I know they have mass, very little mass but they have. When something has mass it must be attracted by gravity and other ...
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2answers
37 views

Why does electromagnetic induction creates both voltage and current but static electricity only creates voltage and no current?

Why is it that electrons do not move the same way in triboelectric as in magnetic induction when both creates voltage? Triboelectricity can even create tens of thousands of volts like Van De Graf ...
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0answers
48 views

Sum rule and dense limit

Is the finite size of lattice constant important for derivation of sum rules, for example, the sum rule for diagonal conductivity $\sigma_{xx}$: $$ \int \limits_{-\infty}^{\infty} d\omega\sigma_{xx}(\...
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0answers
75 views

World's Largest Radio Telesope : How accurately does it need to be figured?

In Guizhou Province, China, the worlds largest radio telescope is almost complete, measuring 500 metres across. I am aware that todays largest optical telescope require very accurate figuring and ...
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1answer
75 views

Schrödinger-Pauli Equation Solutions

The Schrödinger-Pauli equation is the non-relativistic limit of the Dirac equation, and therefore describes spin-1/2 particles in an external electromagnetic field. It is given by: $$\left[\frac{1}{...
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Variation of spin in the rest frame of an electron in an external magnetic field

In Jackson's Classical Electrodynamics, the equation of motion for the angular momentum $\textbf{s}$ of an electron in an external magnetic field is given by (eq. 11.101) $$\left(\frac{d\textbf{s}}{dt}...