Plasma - Ms-Kelly

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16 Νοε 2013 (πριν από 3 χρόνια και 1 μήνα)

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Plasma

What Is It?


A hot ionized gas


The ‘fourth state of matter’


Unlike gases, solids, or liquids, plasma does not
contain molecules


Instead, it is a gas that is composed of ions


Composes more than 99% of the known visible
universe

So What’s In It?



Some, or all, of the electrons in the outer
orbitals have been stripped away



The result is a collection of ions and
electrons, which are no longer bound
together


What Did That Mean?



Because the particles are not neutral:


Plasma behaves differently then regular
gases


For instance, in the presence of
electromagnetic fields

Who Found It?



First discovered by Sir William Crookes, in
1879



But it wasn’t called ‘plasma’ until 1928,
when Irving Langmuir coined the term

Characteristics:
Temperature


Defines two kinds of plasma:
Cold

and
Hot


Refers to the electron temperature


Ion temperature may be very different (lower)





Lightning

is an example of plasma present at
Earth's surface. Typically, lightning discharges
30,000 amperes, at up to 100 million volts, and
emits light, radio waves, X
-
rays and even
gamma rays.

Cold Plasma


Isn’t really cold


Typical electron temperatures for cold plasmas are in
the thousands of degrees


Only a small fraction of the gas molecules are
ionized (degree of ionization)


Usually on the order of 1%


Often created using strong electric fields

Cool

Where Can I Find Cold Plasma?



Fluorescent Lights



Strobe Lights



Experimental Fusion
Research Devices

Hot Plasma


Really hot


Like the Sun (15,000,000
°

C at the core)


The molecules are nearly if not fully
ionized


Created by heating the molecules to
extremely high temperatures

Scorching

Where Can I Find Hot Plasma?


In Nature, actually


The Sun and other stars


Lightning


The Aurora Borealis

Characteristics:
Potentials


Plasmas are excellent conductors


Simple view:


Due to the above, the electric fields in
plasmas tend to be very small


Quasineutrality:


On the one hand, we can assume that
densities of positive and negative charges are
equal


However, we can assume that electric fields
exist as needed for the physics at hand

An Application:

Let’s Get Hands On (sort of)


Plasma Globes


An electrode sitting inside a vessel containing
some kind of inert gas


The electrode is energized by a high
-
voltage,
high
-
frequency power supply


This globe uses voltages around 10 000 volts,
and frequencies ranging from a few kilohertz
to a few 10’s of kilohertz