Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

A plasma is typically an ionized gas

  1. Apr 2, 2006 #1
    from wikipedia:
    "a plasma is typically an ionized gas, and is usually considered to be a distinct phase of matter. "Ionized" in this case means that at least one electron has been dissociated from a proportion of the atoms or molecules."

    1. Since electrons has been dissociated only but not associated, so are all plasmas positively charged?

    "Plasma typically takes the form of neutral gas-like clouds or charged ion beams..."

    2. Plasmas carry charges. So why is it neutral?

    Sorry for my un-up-to-standard questions...
  2. jcsd
  3. Apr 2, 2006 #2


    User Avatar

  4. Apr 2, 2006 #3


    User Avatar
    Staff Emeritus
    Science Advisor
    Education Advisor

    Just because an electron has been stripped from an atom doesn't mean the electron just disappear. It is still in the gas. Thus, the whole plasma is neutral.

    The same thing happens in your ordinary conductor. The conduction electrons are mobile and do not belong to a particular atom. Yet, the whole conductor remains electrically neutral.

  5. Apr 2, 2006 #4


    User Avatar
    Staff Emeritus
    Science Advisor

    Supplementing what Mk and ZapperZ mentioned, plasmas are hot - really hot. Hydrogen plasmas for fusion are heated to the keV range and remember that 1 ev ~ 11605 K, so 1 keV ~ 11605000 K.

    OK, what is the ionization energy of the hydrogen atom? 13.6 eV.

    Well 1 keV >> 13.6 eV, so it's pretty easy to keep a hydrogen atom ionized by virtue of collisions.

    Keep in mind that + and - charges attract - the Coulomb force. Protons don't like their electrons to go to far. If the electron escapes, i.e. chases after another proton or other positive charge, the proton left behind looks for another electron. Protons are not very particular - all electrons 'look' the same to a free proton. :biggrin:

    If there were multiple positive charges in a plasma, those positive charges would repel one another until neutrality was obtain, really until a single + charge remained, and that + charge would be very attractive to a lone - charge.

    The high temperature of the plasma are why the plasma has to be maintained in a magnetic field. The plasma is way too hot for any solid material.
Share this great discussion with others via Reddit, Google+, Twitter, or Facebook