Which term refers to a series of coloured lines observed against a dark background?

The term that refers to a series of coloured lines observed against a dark background is known as a line spectrum. This phenomenon occurs when light emitted from an atom or a molecule is passed through a prism or diffraction grating. The energy levels of electrons in the atoms result in the emission of light at specific wavelengths, leading to the appearance of distinct lines representing those wavelengths.

In a line spectrum, each line corresponds to a particular transition of an electron between energy levels. The dark background contrasts with the visible lines, making it easier to identify each specific wavelength of light emitted. This is fundamentally important in spectroscopy, as it allows scientists to analyze the composition of various elements based on the unique patterns of lines produced for different substances.

The other terms represent different phenomena. A continuous spectrum would show a smooth transition of colors without any distinct lines, while an absorption spectrum displays dark lines within a continuous spectrum where certain wavelengths are absorbed by a substance. An emission spectrum consists of bright lines on a dark background but does not focus exclusively on the specific characteristics of the observed series of coloured lines as the line spectrum does. Thus, the line spectrum is specifically characterized by its distinctive lines against a dark backdrop.