Radiation Laws

Kirchoff's Laws
  1. First Law: A hot solid, liquid, or dense gas emits radiation at all wavelengths ("a continuous spectrum of radiation"). For example, a perfect blackbody does this. If the light were passed through a prism, you would see the whole rainbow of colors in a continuous band.
  2. Second Law: A thin hot gas in front of a cooler background emits radiation at a discrete set of isolated wavelengths. These discrete, isolated wavelengths are called the "emission lines" of the spectrum, because if you were to pass the radiation through a prism, you would see isolated lines of different colors. The whole spectrum is called an "emission-line" spectrum. The wavelengths of the emission lines are unique to the type of neutral atom or ionized atom that is producing the emission lines.
  3. Third Law: A thin cool gas in front of a hotter solid, liquid, or dense-gas background removes the radiation from the background source at special wave lengths. If the resulting radiation were passed through a prism, there would be dark lines superimposed on the continuous band of colors due to the background. These dark lines are called "absorption lines." The wavelengths of the absorption lines are unique to the type of neutral atom or ionized atom that is producing the emission lines.
  4. If a certain type of gas produces absorption lines at certain wavelengths when it is in front of a hot background, then when that same type of gas is seen in front of a cooler background, it produces emission lines at the exact same wavelengths.
Explanation of Kirchoff's First Law Explanation of Kirchoff's Second and Third Laws

Question: An astronomer studying a particular object in space finds that the object emits light only in specific, narrow emission lines. The correct conclusion is that this object

Interesting points about Kirchoff's Laws Role of temperature. Question: The star P Cygni (in the constellation Cygnus, the Swan) is surrounded by an extensive low-density atmosphere. Its spectrum consists of a bright, continuous spectrum with many dark narrow absorption lines and a few bright emission lines. The bright continuous part of the spectrum is produced by