Matter & Energy

Matter is composed of atoms or groups of atoms called molecules. The arrangement of particles in a material depends on the physical state of the substance. In a solid, particles form a compact structure that resists flow. Particles in a liquid have more energy than those in a solid. They can flow past one another, but they remain close. Particles in a gas have the most energy. They move rapidly and are separated from one another by relatively large distances.

Conduction in Gases

Gases normally contain few free electrons and are generally insulators. When a strong potential difference is applied between two points inside a container filled with a gas, the few free electrons are accelerated by the potential difference and collide with the atoms of the gas, knocking free more electrons. The gas atoms become positively charged ions and the gas is said to be ionized. The electrons move toward the high-potential (more positive) point, while the ions move toward the low-potential (more negative) point. An electric current in a gas is composed of these opposite flows of charges.