Unit of length convenient for measuring wavelengths of electromagnetic radiation. Named after the Swedish physicist Anders Jonas Ångström (1814-1874), a founder of Technique of splitting electromagnetic radiation (light) into its constituent wavelengths (a spectrum), in much the same way as a prism splits light into a rainbow of colors. Spectra are not smooth but punctuated by 'lines' of absorption or emission caused by interaction with matter. The energy levels of electrons in. 1 Å = 10-10 m. Most of the visible spectrum lies in the 3900-7500 Å range. Not an SI unit, though it is considered part of the metric Definable part of the universe that can be open, closed, or isolated. An open system exchanges both matter and energy with its surroundings. A closed system can only exchange energy with its surroundings; it has walls through which heat can pass. An isolated system cannot exchange energy or matter with.