# 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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### Why is Terahertz radiation so hard to generate?

This paper (and many others I've read) claim that searching for ways of producing THz radiation is a high-interest research topic. However, something I've just never understood is why it's so hard ...
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### Is what i think Magnetism is, Magnetism? [closed]

So, i was randomly thinking about magnets one day and decided to try and figure out what Magnetism actually is. This is what i came up with: Magnetism, the magnetic field of an object, is a form of ...
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### Physical significance of toroidal moments

The electric field of a toroidal dipole moment $\vec t$ is the same as the electric field of a electric dipole moment $\vec p$, except that it is scaled with the factor $ik$. The $i$ makes the ...
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### Separating aluminium sheets with magnetic field

all! I would like to know if it would be possible to induce a strong enough magnetic field in sheets of aluminium so they would be separated between each other, like when you use magnets to separate ...
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### Why does charge build up at the boundary surface of two media?

On a homework problem, we are asked to to use the first two Maxwell equations, $$\nabla\cdot \mathbf{B} = 0$$ $$\nabla \cdot \mathbf{D} = \rho$$ to show that along the boundary surface of two ...
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### How did Lenz derive his law?

I read about it but am not sure if it actually follows law of conservation of energy.I tried reading some reference books but could not find the derivation of the law.
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### What does an induced emf do to a loop of varying current?

I know that the magnetic flux through a loop in space is proportional to the current such that $\Phi=LI$. Therefore a change in magnetic flux will produce an emf, so $\mathscr{E}=-L\dfrac{dI}{dt}$. ...
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### Why breakdown voltage decreases with increasing FWHM of an asperity?

I am running a simulation for a dielectric breakdown. I am getting breakdown voltage decreases with FWHM, which does not make sense as field enhancement is higher for a small width. Simulations solve ...
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### Do Ampère's and the the Biot-Savart law give different answers for the magnetic field of a circular loop? [duplicate]

I have been trying to calculate the magnetic field due to a circular loop using Ampère's circuital law. However, I am unable to do the same. Whenever I apply the law, while integrating length ...
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### How can we define the energy stored in a (conservative) force field?

I have come to know from my textbook that energy is stored in the E-field of a capacitor, in the B-field of an inductor and so on. Take the example of an inductor. The derivation bewilders me ...
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### Where did earth's electric charge come from?

I get between .7 and 1.3 volts out of a 20 foot tree depending on the weather. I understand this is "telluric" electricity with pretty low amperage. Where is this charge coming from? The sun, right? ...
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### Why is Bose-Einstein condensation a phase transition?

Bosons may succumb to a Bose-Einstein condensation at a certain critical temperature $T_c$, thus entering the BEC phase. The only thing I know about the BEC is that since we are talking about bosons ...
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### Did light already experience death of the universe immediately after the Big Bang?

Let's suppose that I am on Point A with a light-beam launcher. My goal is to launch a beam of light to Point B, which is about 8,000 quadrillion light years away. My friend named Jack is at Point B ...
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### Field Vectors and satisfying Maxwell's equations

If I have an electric field that its direction is parallel to the direction of the wave propagation, it will not satisfy Gauss's law for vacuum. However we can say it satisfies Gauss's law for non-...
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### Extremely long wavelength electromagnetic radiation

High frequencies are used to eject electrons, because only electrons can really be affected at such a small wavelength scale. But could an electromagnetic wave have such a ridiculously low frequency (...
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### How to experimentally reconstruct Maxwell's equations from scratch

What are the minimal experiments would one need to perform in order to reconstruct Maxwell's equations from scratch, assuming even the concepts of $\vec E$ and $\vec B$ are unknown? While I'm not ...
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### Magnetic Field Direction — a single one — on a current carrying wire

Take the wire on the right hand side. It experiences a force to the left of the page. To experience a force pointing left-wards, the magnetic field must point into the page. Why does it point into the ...
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### Do the integral forms of Maxwell's Equations have limited applicability because of retardation?

In the usual bookwork treatment, it is easy to show that the differential and integral forms of Maxwell's equations are equivalent using Gauss's and Stokes's theorems. I have always thought that ...
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### Is there something equivalent to a diode for light?

In electronics a diode is a component allowing current passing in only one direction, and blocking the other side. I'm wondering if something similar exists for visible light or other EM waves, like ...
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### Can a magnetic field be focused at a distance?

There are interesting arrangements of magnets that can strengthen the field in some places while weakening it in others. This is discussed in Can magnetic fields be redirected and focused at one point?...
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### Does the induced Electric field develop instantly or lags by $\frac rc$?

Consider a loop of radius $r_0=3 \times 10^8$ cm. A thin bar magnet is passed through its center. This implies that the magnetic flux through the loop will change. Now according to Faraday's law a non ...