- For a mathematically rigorous point of view of "discrete spectrum", see decomposition of spectrum .
In physics, an elementary (and accurate) explanation of a discrete spectrum
is that it is an emission spectrum
or absorption spectrum
for which there is only an integer number (or countable
number) of intensities. Atomic electronic absorption and emission spectrum are discrete, as contrasted with, for example, the emission spectrum of the sun, which is continuous. Discrete emission spectra of atoms are also referred to as emission line spectra, which show vertical lines at the frequencies (or wavelengths) of emission. To describe the difference between continuous and discrete spectra, we might refer to probability theory—measuring weight versus throwing dice.
Conceivably, our body-weights can be represented by any number, 50.00000 kilograms, 59.99999 kg, 39.999591 kg, the number of decimals determined by our equipment, not by any fundamental restriction on the value of a weight. By contrast, when we throw dice, the throw of a single six-sided die can yield only 1, 2, 3, 4, 5, or 6, and nothing in between; there is a fundamental restriction on the numbers we can get throwing a single die; we cannot get a 3.2, 4.5, or 1.7; we can only get whole numbers between 1 and 6 inclusive. The set of all possible weights is continuous; the set of all possible single-die tosses is discrete.
One segment of the emission spectrum of atomic hydrogen is shown below.... Read More