Matter commonly exists in three states: solid, liquid, and gas. Plasma is often referred to as the fourth state of matter, a highly energetic form derived directly from gas. Adding sufficient energy to a gas causes its fundamental structure to change, transforming it into plasma. Understanding this connection requires examining the points of overlap and the differences that make plasma a unique medium.
The Microscopic Difference Between Gas and Plasma
The fundamental distinction between a gas and a plasma lies in their internal particle composition. A neutral gas consists primarily of atoms or molecules that are electrically neutral overall, maintaining a balance of charged nuclei and electrons. These particles are not significantly influenced by long-range electromagnetic forces.
Plasma is created through ionization, where enough energy strips electrons from the neutral atoms or molecules. This results in a mixture of positively charged ions and unbound, negatively charged free electrons. The presence of these charged particles transforms the neutral gas into plasma, setting the stage for subsequent differences in behavior.
Macroscopic Properties Shared by Gases and Plasmas
Gases and plasmas share several macroscopic physical properties because they both belong to the category of non-condensed matter. Neither state possesses a fixed volume or a definite shape; both gas and plasma will expand to completely fill any container they occupy. This characteristic allows them to be classified as fluids.
Both states are highly compressible, as the particles are separated by large amounts of empty space. This low density permits a significant reduction in volume when external pressure is applied. Their particles move randomly, allowing both gases and plasmas to exhibit pressure and flow according to similar principles of hydrodynamics.
Unique Electrical and Magnetic Behavior of Plasma
The presence of free charged particles gives plasma unique properties that a neutral gas cannot exhibit. Plasma is an excellent electrical conductor, behaving much like a metal, whereas a neutral gas acts as an electrical insulator. This high conductivity means that even a small electric field can generate significant currents within the plasma.
The charged nature of plasma causes it to interact strongly with magnetic fields, a phenomenon virtually absent in neutral gases. Magnetic fields can be used to confine, shape, and manipulate plasma, which is a core strategy in fusion energy research. Unlike neutral gas particles that interact mainly through short-range collisions, plasma particles influence one another over large distances via electromagnetic forces.
This long-range electrical influence leads to collective behavior, a defining trait of plasma physics. The charged particles effectively shield any local electric field through a rapid reorganization of ions and electrons. This shielding means that the behavior of one particle is closely coupled to the motion of many distant particles, allowing plasma to support complex waves and instabilities.
Where Gases and Plasmas Exist in the Universe
The location of gases and plasmas is largely determined by the amount of energy present in an environment. Gas is common in lower-energy, terrestrial environments, forming the atmosphere of Earth and utilized in many industrial and chemical processes. It is the dominant state of matter in conditions typically encountered on our planet’s surface.
Plasma, conversely, is the most common state of visible matter in the universe, estimated to account for over 99% of it. The extreme temperatures and pressures within stars, such as the Sun, ensure that their matter exists as plasma. Vast regions of space, including nebulae, the solar wind, and the space between galaxies, are also filled with plasma.
On Earth, plasma typically requires a significant energy input to be maintained, such as the high-voltage electricity used in neon signs or plasma televisions. Natural terrestrial examples, like lightning and the auroras, are relatively fleeting. The energy difference required to sustain the ionized state of plasma versus the neutral state of gas is the primary factor dictating their universal distribution.