The kind of atoms or molecules are present and their relative abundance can be determined by observing wavelengths.
Wavelength is the distance between adjacent crest or trough of the wave.
The light travels in the form of wave and particle. It behaves like both. Light ray consist energy of the photons. The kind of atoms or molecules present behave like particle and they have particular wavelength.
Thus, by observing wavelength , we can determine the kind of atoms or molecules are present and their relative abundance.
Learn more about wavelength.
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