The sodium D lines are a closely spaced pair of spectral lines in neutral sodium. They are present as absorption lines in the spectrum of the Sun's photosphere because of traces of sodium there. What would one expect to see if sunlight is passed through a cool sodium vapor in the laboratory and then observed with a spectroscope?
A) The sodium D lines will become brighter.
B) The sodium D lines will become darker.
C) The two absorption lines will merge into a single line.
D) The position of the sodium D lines will shift to a lower frequency.

Question

Quizplus · Accepted Answer

When sunlight, which already contains the sodium D absorption lines, is passed through a cool sodium vapor, the sodium atoms in the vapor will absorb the same wavelengths of light, making the sodium D lines appear darker in the observed spectrum. This is due to the increased absorption at those specific wavelengths by the sodium atoms in the vapor.

The Sodium D Lines Are a Closely Spaced Pair of Spectral