# Tagged Questions

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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### 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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### 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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### 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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### 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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### 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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### 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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### 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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### 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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### 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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### 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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### 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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### 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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### 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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### 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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### 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 ...
Is the finite size of lattice constant important for derivation of sum rules, for example, the sum rule for diagonal conductivity $\sigma_{xx}$: $$\int \limits_{-\infty}^{\infty} d\omega\sigma_{xx}(\... 0answers 75 views ### World's Largest Radio Telesope : How accurately does it need to be figured? In Guizhou Province, China, the worlds largest radio telescope is almost complete, measuring 500 metres across. I am aware that todays largest optical telescope require very accurate figuring and ... 1answer 75 views ### Schrödinger-Pauli Equation Solutions The Schrödinger-Pauli equation is the non-relativistic limit of the Dirac equation, and therefore describes spin-1/2 particles in an external electromagnetic field. It is given by:$$\left[\frac{1}{...
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}...