In a spectrum with dark lines on a continuous background, what term describes that spectrum?

• A. Emission line spectrum
• B. Absorption line spectrum
• C. Continuous spectrum
• D. Line spectrum

Answer: (B)

This type of spectrum shows a continuous background with dark gaps where light has been removed by absorption. When a hot, dense source emits a broad, smooth spectrum and its light passes through a cooler, diffuse gas, atoms in that gas absorb photons at specific wavelengths that match their electronic transitions. Those absorbed wavelengths appear as dark lines against the bright continuum, giving an absorption line spectrum. Emission line spectra would show bright lines on a dark background, and a continuous spectrum lacks lines altogether. So the correct term for dark lines on a continuous background is an absorption line spectrum.