Questions tagged [electromagnetism]
The classical theory of electric and magnetic fields, both in the static and dynamic case. It also covers general questions about magnets, electric attraction/repulsion, etc. Distinct from electrical-engineering.
19,762 questions
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How do moving charges produce magnetic fields?
I'm tutoring high school students. I've always taught them that: A charged particle moving without acceleration produces an electric as well as a magnetic field. It produces an electric field ...
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127votes
13answers
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Can Maxwell's equations be derived from Coulomb's Law and Special Relativity?
As an exercise I sat down and derived the magnetic field produced by moving charges for a few contrived situations. I started out with Coulomb's Law and Special Relativity. For example, I derived the ...
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How can I stand on the ground? EM or/and Pauli?
There is this famous example about the order difference between gravitational force and EM force. All the gravitational force of Earth is just countered by the electromagnetic force between the ...
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Does the $\frac{4}{3}$ problem of classical electromagnetism remain in quantum mechanics?
In Volume II Chapter $28$ of the Feymann Lectures on Physics, Feynman discusses the infamous $\frac43$ problem of classical electromagnetism. Suppose you have a charged particle of radius $a$ and ...
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5answers
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How and why do accelerating charges radiate electromagnetic radiation?
Let's consider it case by case: Case 1: Charged particle is at rest. It has an electric field around it. No problem. That is its property. Case 2: Charged particle started moving (it's accelerating)....
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Can tin foil hats block anything?
This is joked about all the time, but... Can tin foil hats actually block anything? If they can, what frequencies? Is there any research into tin or aluminum foil and radio blocking or amplifying ...
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89votes
7answers
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Do Maxwell's Equations overdetermine the electric and magnetic fields?
Maxwell's equations specify two vector and two scalar (differential) equations. That implies 8 components in the equations. But between vector fields $\vec{E}=(E_x,E_y,E_z)$ and $\vec{B}=(B_x,B_y,B_z)$...
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What is the mechanism behind the slowdown of light/photons in a transparent medium?
So light travels slower in glass (for example) than in a vacuum. What causes light to slow down? Or: How does it slow down? If light passes through the medium, is it not essentially traveling in the "...
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89votes
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How can magnets be used to pick up pieces of metal when the force from a magnetic field does no work?
I learned that the force from a magnetic field does no work. However I was wondering how magnets can be used to pick up pieces of metal like small paperclips and stuff. I also was wondering how ...
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85votes
4answers
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If you are vacuuming your carpet and you wrap the cord around your body do you become a magnet?
If you wrap an active electric cord around your body, do you become an electromagnet?
79votes
4answers
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How exactly is a normal force exerted, at the molecular level?
I've been surfing the web for quite a while, finding the answers I would need, but couldn't find a convincing one. First of all I need to remind you that this a very long/continuous question, so ...
user226894
76votes
3answers
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Why don't the Earth's oceans generate a magnetic field?
Many questions have been asked here about why the Earth has a magnetic field, e.g., What is the source of Earth's magnetic field? How does Earth's interior dynamo work? How can an ...
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If like charges repel, why doesn't a charge break itself apart?
How can it be that, if like charges repel, they don't repel themselves? In other words, why don't charges break apart? About the possible duplicate: I want to know about charges in general, not just ...
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What's the physical meaning of the statement that "photons don't have positions"?
It's been mentioned elsewhere on this site that one cannot define a position operator for the one-photon sector of the quantized electromagnetic field, if one requires the position operator have ...
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