is flame a plasma?

Question

is candle flame a plasma? (what even is plasma?)
i’ve always wanted to know what really is a flame… is it plasma? is it magic?
what is it? i know it’s a chemical reaction with the oxygen in the air.

In: 201

Answer 1

> (what even is plasma?)

Well, the first thing to ask is what do people mean when they say ‘liquid’ or ‘gas’. And here the definitions you learned in elementary school are probably correct. When you say ‘gas’ what you mean is a bunch of material that follows the ‘rules’ for a gas. So you can predict how a specific gas by applying the general gas rules. ‘Plasma’ is a new state because it no longer follows ‘gas’ rules.

More specifically a plasma is a ‘gas’ where a sufficiently large number of ions exist to cause significant interactions with electromagnetic fields. Because of this new mode of interaction a lot of assumptions that are made for ‘gas’ don’t hold true for ‘plasmas’.

For example, bits of plasma can interact with each other at ‘long’ distances.

Imagine you wanted to predict the behavior of say a big cloud of helium gas on the atomic scale on a computer. You could arrive at a pretty decent solution by treating each helium atom as a ball, and just simulating those balls bouncing off each other when they ‘hit’. The nice thing about this is when you’re trying to simulate each atom you only need to worry about the handful of other atoms that are close enough to trigger a collision.

Now lets say you ionize some of those helium atoms to make an helium plasma. Now you have a mix that includes free electrons (e-) and helium ions He+. These are still going to ‘bounce’ the same way the neutral atoms did, but there is a significant complication. When you take an ion and cause it change direction/speed you create an EM field. EM fields will also interact with ions that are traveling in them. So now, when your He+ ion bounces off something you can’t just look at the few closes atoms to see what effect it has, you would need to look at how it effects all the ions in your simulation.

Similarly a ‘gas’ will not respond to an externally applied field, but a plasma will. This allows a plasma to conduct electricity. It also means that it’s possible for two plasmas to ‘couple’ at non-trivial distances (e.g. two plasmas can have significant effects on each other beyond ‘touching’ distance by shooting EM fields at each other).