20. Fraunhofer lines are dark lines in the solar spectrum. They arise because
a. the sun consists mainly of hydrogen and helium, which do not emit a
continuous spectrum.
b. the sun’s outer regions contain other elements which emit various
wavelengths, making the spectrum uneven.
c. gases in the sun’s outer region absorb specific wavelengths.
d. the absorption of specific wavelengths by gasses in the Earth’s
atmosphere.
Correct Answer
Fraunhofer lines arise because gases in the sun’s outer region absorb specific wavelengths.
Option Analysis
Option a: the sun consists mainly of hydrogen and helium, which do not emit a continuous spectrum.
This is incorrect. The sun’s photosphere emits a continuous spectrum due to its high temperature, despite being mainly hydrogen and helium; the dark lines result from absorption, not lack of emission.
Option b: the sun’s outer regions contain other elements which emit various wavelengths, making the spectrum uneven.
This is wrong. Emissions would create bright lines, not dark ones; Fraunhofer lines form from absorption, not emission, by cooler gases overlaying the continuous spectrum.
Option c: gases in the sun’s outer region absorb specific wavelengths.
This is correct. Light from the hot photosphere passes through cooler chromosphere gases, which absorb specific wavelengths, producing dark absorption lines known as Fraunhofer lines.
Option d: the absorption of specific wavelengths by gasses in the Earth’s atmosphere.
This is incorrect. While Earth’s atmosphere causes some telluric lines (e.g., A, B), most Fraunhofer lines originate from solar atmosphere absorption, as confirmed by lab-matching emission spectra.
Introduction
Fraunhofer lines solar spectrum reveal dark absorption lines due to gases in the sun’s outer region absorbing specific wavelengths from the hot photosphere’s continuous spectrum. These lines, named after Joseph von Fraunhofer, act as chemical fingerprints for solar composition analysis in astronomy. Understanding Fraunhofer lines solar spectrum aids CSIR NET Life Sciences and physics exam preparation.
