Which type of spectrum is produced by hot, dense objects?

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

Answer: (D)

Thermal radiation from a hot, dense object produces a continuous spectrum because the myriad atoms and molecules emit photons across essentially every wavelength, and those emissions overlap to form a smooth curve without gaps. This is the blackbody-like behavior of dense matter, where many possible transitions fill in all the wavelengths. In contrast, emission spectra from sparse gases show discrete bright lines at specific wavelengths, since only certain energy transitions occur. Absorption spectra arise when a hot source shines through cooler material that absorbs particular wavelengths, creating dark lines in an otherwise continuous spread. So a hot, dense object gives a continuous spectrum.