Questions tagged [plasma-physics]

Theory, lab and space experiments, and calculations related the physics of plasmas, i.e., matter constituted by ionized atoms.

The critical conditions necessary for a medium containing charged particles to be considered a plasma are:

  • the collection of particles in a given volume, typically a Debye sphere, exhibit a collective fluid-like behavior;
  • the Debye length be much smaller than the system size (i.e., avoid boundary/edge effects); and
  • the plasma frequency be much larger than the collision rate between electrons and neutral particles.

Wikipedia has a rather large list of topics related to plasmas.

When to Use this Tag

covers the physical description of plasmas (ionized media). It should be distinguished from . It can be combined with other tags such as or to specify what type of plasmas are involved.

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What is the speed of sound in space?

Given that space is not a perfect vacuum, what is the speed of sound therein? Google was not very helpful in this regard, as the only answer I found was $300\,{\rm km}\,{\rm s}^{-1}$, from Astronomy Cafe, which is not a source I'd be willing to…
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Is fire plasma?

Is Fire a Plasma? If not, what is it then? If yes why, don't we teach kids this basic example? UPDATE: I probably meant a regular commonplace fire of the usual temperature. That should simplify the answer.
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What is happening when magnetic field lines snap or break?

In discussions of sun spots and auroras on Earth, magnetic field lines are often described as "snapping" or "breaking", with the result of releasing charged particles very energetically. My understanding is that field lines are just a visualization…
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Why does only one side of a neon lamp glow?

When applying DC to a neon lamp, only the negatively-charged electrode glows: The voltages across the lamps are left: DC (left lead positive), middle: DC (right lead positive), and right: AC. But... why? The electrodes are the same shape, so the…
endolith
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Why do we deal only with large scale magnetic fields in astrophysics, and not electric fields?

In astrophysics there is a lot going on about strong, large scale magnetic fields: in stars (prominences), magnetic dynamos, compact accretors collimating jets, etc. There's even a special computational formalism called magnetohydrodynamics (MHD),…
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What are these alternating bright and dark rings in fluorescent lamp?

I'm quite surprised by these regularly spaced rings of alternating brightness in a fluorescent tube. These are also moving along the tube and only appear when the voltage is low. What are these and does the pattern have anything to do with AC…
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Why is a stellarator-type nuclear fusion reactor so oddly-shaped?

My first impression: It's a mess. Why is it shaped like that? I can't find any info about its shape other than it's a special arrangement of magnetic coils.
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How can a star emit light if it is in Plasma state?

I understand that star is in Plasma state (all nucleus and electrons are not bound to each other and moving around freely) Photon is emitted when an excited electron moves back to lower orbit. So in a star if electrons are not in any orbit then how…
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What is the safe distance to a supernova explosion?

In other words, what stars near the Sun may have an impact on the Solar system equilibrium or the Earth life if they become supernova ? Is SN 1987 A too far ?
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What causes fluorescent light bulb to light up when it is near a plasma globe? Can this phenomenon be used to generate electricity in a circuit?

When a fluorescent light bulb is placed near a plasma globe, despite the fact there isn't a closed circuit, a part of the light blulb would light up. I tried measuring the voltage of the air around it with the probes of a multimeter, and…
user21936
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Does Fire Conduct Electricity? Why?

Recently, I have stumbled upon a YouTube video by Veritasium describing the conductivity of fire. My question is: how exactly does fire conduct electricity? I am a high school student; therefore appropriate language is expected.…
PotatoIn
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Why all the orifices, protuberances, hinged/bolted panels, etc. on a stellarator?

My question was inspired by this one - in particular the image it has (also shown here): Why does the external casing of the Stellarator (in particular, the Wendelstein 7-X shown in the above image) have so many orifices, hinged/bolted panels,…
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Why were space physicists wrong about the location of the heliopause?

The heliopause is now estimated to be something around 100 AU (1 AU = Astronomical unit = about the earth sun distance). See the wikipedia article: http://en.wikipedia.org/wiki/Heliosphere From reading a book on NASA's Voyager mission, I learned…
Carl Brannen
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How is a plasma different from a metal or an ionized gas?

I've just started looking at plasmas and I have some confusion. A metal is a lattice of positive ions bathed in a sea of delocalised electrons and conducts electricity. A plasma is a 'gas' of free ions and electrons and can also conduct electricity.…
Jabeaumes
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Is there a phase transition between a gas and plasma?

Does a phase transition occur as a gas is heated to create a plasma? If so, is this a first or second order phase transition? Also, does the presence of a phase transition depend on the pressure or composition? It seems to me that in the dilute…
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