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Results tagged with electromagnetism
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user 356606
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.
1
vote
Accepted
Current density in the presence of a stationary point charge of varying magnitude
Your result for the current density actually looks right to me. Your charge suddenly appears at $r=0$, but it doesn't come... from anywhere. Or in other words it has to come from infinitely far away a …
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1
vote
Accepted
Question about Ionization energy and Potential energy
The specific qualm you have about this rule is resolved by the words "absolute value" - the potential energy becomes less negative (bigger), and the ionization energy gets less positive (smaller) when …
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3
votes
What would happen to the electric field if the charge it produced suddenly disappeared?
Curious what other people have to say - this might not be the only/a complete answer.
I'd say the answer is undefined (or perhaps it doesn't matter). Charge conservation is baked into the Maxwell equa …
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2
votes
Accepted
Can high energy photons be used to accelerate particles?
It's not easy, but definitely possible, for free charged particles. Scattering of a photon off of an electron at rest can be most easily understood in the center-of-mass frame with zero total momentum …
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12
votes
The physics behind a homemade particle accelerator
Yes, in this video the centripetal acceleration is provided by the tube. This is kind of overcomplicated language for "the tube is the only reason the ball follows a circular path." The magnetic coil …
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1
vote
Gyrating proton near magnetic pole of the Earth
Let's call the cyclotron (angular) frequency $\omega$, the cyclotron/Larmor radius $r$, the velocity perpindicular to the magnetic field $v_\perp$, the particle charge $q$ and mass $m$. The angular mo …
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1
vote
Why is there no electron-positron plasma around proton?
Interesting question. I wasn't previously aware of this way of explaining a few effects. In the end, I conclude that the effect you're describing should give rise to (1) a small perturbation to the pr …
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11
votes
Accepted
How can it be "unfortunate" while this is what the experiments want?
This is "unfortunate" because if you want to use a particle accelerator to probe deeper laws of nature, it needs to accelerate particles to as high energy as possible, not just "any decent fraction of …
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3
votes
Why should we expect motional emf to obey the same general relation as Faraday's Law?
Let's say you have a small loop sitting right at the end of a solenoid
The following two situations should induce the same current in the loop:
The solenoid's current is turned down
The solenoid is …
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6
votes
Accepted
Doubt regarding a possible mistake in Griffiths Electrodynamics
Griffiths is right. Don't forget that that current flows outward on the plate to spread out the charge. The charge density on the plate is $\sigma=It/A$. In order to reach the area outside of $A'$ it …
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1
vote
Magnetostatics or dynamics?
This is indeed magnetostatics. The question is about an equilibrium charge distribution. The charges are moving, and this produces a current, but that current and the charge distribution are constant. …
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1
vote
Accepted
Catastrophic absorption by carbon dioxid in atmosphere: value of the polarizability
This YouTube video goes into depth about the real explanation of global warming. Indeed, as you point out, infrared radiation from the earth is always absorbed and reemitted in the atmosphere many tim …
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3
votes
Accepted
Does the magnetic field, circulating the moving uniformly charged sphere, exert force/tensio...
Yes test charges on the surface of the moving charged sphere feel this force. Yes it affects the strain of the sphere of charge in the lab frame.
But don't forget that some external forces are needed …
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0
votes
Energy increase due to the Zeeman effect
$\mu$ parallel to $B$ is the lower energy state (the one with a negative energy). In some conventions this might mean spin is anti-aligned with $B$ if $\mu$ points the opposite direction of spin becau …
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0
votes
Does the charge distribution of two uniformly charged conducting spheres change as we bring ...
Some of your question can be answered conceptually. A uniformly charged sphere on its own is an equipotential surface, and it makes a potential outside of itself of $(1/4\pi\epsilon_0)Q/r$. Thus if tw …
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