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26

Many astrophysical plasmas are well modeled as perfect conductors. Ideal MHD assumes this limit. As a result, there is no electric field in the fluid's rest frame. In other frames, we generally have $\vec{E} = -\vec{v} \times \vec{B}$, so there is an electric field. However, the perfect conductivity constraint means we don't have to model the electric field ...


22

Broadly speaking, fire is a fast exothermic oxidation reaction. The flame is composed of hot, glowing gases, much like a metal that is heated sufficiently that it begins to glow. The atoms in the flame are a vapor, which is why it has the characteristic wispy quality we associate with fire, as opposed to the more rigid structure we associate with hot metal. ...


17

Firstly, 'Fire', according to numerous comments and answers [here][1] is a 'process', in which case, the answer to the question will be 'no', since plasma is a state of matter. It would be unfair to leave it there by blaming the semantics, and given the abundant references to 'flame' region, I am going to assume that that is what the question meant to ask. I ...


14

Wet wood crackles. Dry wood does not. Water in the wood boils. The steam builds up pressure because it is trapped inside. The wood explodes, releasing the steam and flying pieces.


14

A brief history of the misapplication of magnetohydrodynamics to the analysis of the solar wind: 1959: Soviet satellite Luna 1 directly observed the solar wind for the first time and measured its strength. http://en.wikipedia.org/wiki/Luna_1 So as of 1959, by direct experimental observation, it was known that the heliopause was at least the radius of the ...


12

Solar wind is neutral overall else the Sun will become globally very strongly charged and we don't see that happening. It comprises Electrons/Protons and other particles.


12

Yes, the claims in the video are totally absurd from the viewpoint of science. It's enough to listen for roughly 70 seconds to be sure that the narrator doesn't have the slightest clue about physics and the remaining 302 seconds make this fact even more self-evident. I won't try to answer the question whether the authors of the video realize that what they ...


12

1.I understand that star is in Plasma state (all nucleus and electrons are not bound to each other and moving around freely) While hydrogen only has one electron, all other neutral atoms have more than one electron. When one electron is removed, this is referred to as the "first ionization". Removing one of several electrons from an atom still makes ...


11

Yes, a plasma contains positive ions and negative electrons, but the positive ions don't need to be atoms. Actually the negative charges don't even need to be electrons. For example, plasma etching of silcon is done using a sulphur hexafluoride plasma that consists of (mainly) SF$_5^+$ and F$^-$ ions. I'm not sure that the word plasma has a precise ...


11

You actually make reference to something which is of crucial importance to the answer to this question: "With a tokamak, I imagine that if you double the linear dimensions, the plasma volume (and hence the power production) will increase eightfold, whereas area that you have to protect against fast neutrons will only quadruple. So once you master the ...


11

The asymmetry comes from the different masses of electrons and neon ions (neon ions are about 36000 times heavier). This mass asymmetry results in different cross sections for the excitation of neon atoms by electrons and ions. There are some plots of this here (figure 1a for electrons, figure 1b for ions). The interesting processes of excitation occur ...


10

It seems to me that you are confonding a generic notion of total derivative and the so called Lagrangian derivative (also known as material derivative). Let us start from scratch. In Cartesian coordinates, a fluid or a generic continuous body is first of all described by a class of differentiable (smooth) maps from $\mathbb R^3$ to $\mathbb R^3$: ...


8

The lack of the electric field in modeling plasmas stems from the Lorentz force, $$ \mathbf F=q\mathbf E+q\boldsymbol\beta\times\mathbf B $$ where $\boldsymbol\beta=\mathbf v/c$. For most astrophysical plasmas, the force is zero, so we have that $$ \mathbf E=-\boldsymbol\beta\times\mathbf B $$ So any time we see an electric field, we can simply replace it ...


8

At atmospheric pressure, air and other gases are poor conductors (Insulators) of electricity. Because, they don't have any free electrons to carry current. But, once the free electrons are produced in gas by ionization (they become plasmas), electric discharge occurs. This could be done in many ways such as by applying a large potential difference across a ...


8

From my cursory overview of the stuff these people have online, there are a few really glaring problems: First and foremost, it doesn't appear that the electric universe model makes any quantitative predictions. I don't see any models for how stars and galaxies are supposed to form and behave, just a bunch of words about how gravitational models make too ...


8

You've actually identified a key area of ongoing research known as the coronal heating problem. First, let's get one thing out of the way. You ask: Or is there a type of matter with thermal conductive properties that could accomplish this? There can be no such material. Any material that passively diffuses heat from a cooler region to a warmer one ...


8

One must be very careful in making the step from $\nabla\cdot\mathbf{B}=0$ to a statement such as "magnetic field lines do not start or end". Consider the field in the region of an X-point type magnetic null (in two dimensions). Take a 'volume' (i.e. an area) centred on the null point, and look at the field lines through the bounding curve. No matter how ...


7

Plasma is a kind of matter very similar to gas in which atoms have been ionized. It is very hot and lets off radiation (also in the visible spectrum) due to recombination so it might already be considered flame. Thus it isn't clear what "igniting plasma" really means. In cold plasma where only a small fraction (few percent) of atoms have been ionized you ...


7

Plasmas are a common part of the world we live in. The definition of plasma allows them to exist within an environment consisting mostly of bound atoms. A variety of human technology creates plasmas. The type I hear plasma researchers reference most is a simple RF Plasma. This is perhaps the most direct way to use electricity to shake off the electrons ...


7

The big problem with controlled fusion is that the equations governing the plasma are highly non-linear. So each time the physicist increase the size of the Tokamak, new effects are discovered. So I guess that the answer is no-one really knows the correct scaling laws ! This contrasts a lot with fission reactors, where the relevant equations are ...


7

You're presumably thinking that vaporised NaCl would consist of Na$^+$ and Cl$^-$ ions, but this isn't what you get. At temperatures just above the boiling point (1413c) you get neutral NaCl molecules and Na$_2$Cl$_2$ dimers, and possibly bigger polymers. Amazingly someone has measured this: see this paper for details (it's behind a paywall I'm afraid but ...


7

There is a difference between temperature and energy. Plasma is, as you said, very hot - but there isn't very much of it. The density of plasma in the tube is very low. So when it does hit the walls of the tube it transfers very little energy. So the mass of the glass tube increases in temperature only very slightly. It's like a firework sparkler, the ...


7

Did you notice the title of the video? Former NASA Physicist Disputes Einstein’s Relativity Theory At the moment main stream physics, which is what we discuss here, does not accept all the various theories trying to unseat General Relativity . Usually these people have an obsession with Einstein or other prominent physicist as personalities . Look at ...


6

Emission of photons can be discrete, as in transitions from one quantized state to another, or continuous. Continuous radiation for example is the synchrotron radiation of electrons moving in magnetic fields in accelerators. Bremsstrahlung is when : is electromagnetic radiation produced by the deceleration of a charged particle when deflected by ...


6

The highest recorded temperature of a plasma is not hotter than nuclear reactions. There is a continuum of phenomena that happen at high temperature that includes and extends beyond nuclear reactions. When temperatures get to be very high, it makes sense to start thinking in terms of the energies involved rather than sticking to the kelvin scale (or ...


6

The Basic Idea Physically the total derivative tells you how a quantity changes when it is subjected to a space and time dependent velocity field. In physics we usually call it the material derivative. An Intuitive Example Suppose $\rho(\mathbb{x},t)$ measures the temperature of a fluid, according to a thermometer immersed at the point $\mathbb{x}$ and ...


6

Bare with me, I don't remember every little step, but I hope this derivation helps you. First remember how a wave travels through a waveguide (dielectric). $$ E(x,y,z) = E^{0}(x,y)e^{-\gamma z}$$ $$ H(x,y,z) = H^{0}(x,y)e^{-\gamma z}$$ Then consider Ampere's and Faraday's Laws for a source-free region. $$ \triangledown \times H = j\omega\epsilon E $$ $$ ...


6

This video illustrates how a candle flame conducts a high voltage (10,000 volts). Although the ion density is small in a candle flame, they are sufficiently present to conduct electricity.


6

See Wikipedia for a list of available plasmas over there..! Or have a look below for the chart which shows variation of temperature and electron density in different plasmas..! A quick Googling would've provided the answer. Common examples include Lightning..! The Sun (from Core to Corona) Fluorescent Lights and Neon Signs Nebulae (Luminous Clouds ...


6

Good question! The defining difference is that in a gas the atoms are intact, and in fact are typically bonded into molecules, whereas in a plasma at least some of the electrons separate entirely from their atoms. In other words, particles of a plasma are charged, but particles of a gas are mostly uncharged. So technically, a plasma is not a gas and it ...



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