When atoms or molecules are excited electrically by an arc or spark, they emit electromagnetic radiation that is characteristic of their component atoms. An instrument for measuring the intensity of radiation at different wavelengths in a spectrum is called a spectrophotometer. The earliest known period of human culture, marked by the use of stone tools. Sublimation Direct transition to the gaseous state from the solid state without passing through the liquid state. Substance A substance has constant composition and properties throughout.
All substances are either elements or compounds.
Superconductor A material that has zero bulk electrical resistance. This mixture is sold as superphosphate . Teflon Teflon,a trademark for a waxy, opague material. It is used as a coating on cooking utensils and in industrial applications to prevent sticking. The junction develops a measurable electric potential which varies with change of temperature.