Why Does a Sodium Vapor Lamp Create a Dark Line at 589nm in the Spectrum?

[maxthedog]

Homework Statement

i understand that the wavelength given off by a sodium vapor lamp is 589nm, is this why there is a dark line in the continuous spectrum at 589mn?

Homework Equations

The Attempt at a Solution

 

[GCT]

Homework Statement

i understand that the wavelength given off by a sodium vapor lamp is 589nm, is this why there is a dark line in the continuous spectrum at 589mn?

Homework Equations

The Attempt at a Solution

Yes and it's actually two lines.

 

[mgb_phys]

i understand that the wavelength given off by a sodium vapor lamp is 589nm, is this why there is a dark line in the continuous spectrum at 589mn?

Yes - electrons move between fixed energy levels in the atom and need a fixed amount of energy to do this. This corresponds to a photon of a particular wavelength.
So if you heat up sodium (give it energy) the electrons can move from the one energy level to another and give off photons of exactly this wavelength.
Similairly if you send light of all wavelengths through sodium onyl those photosn with exactly the correct energy will be used to move an electron upto the other level. So the only photons with the correct wavelength will be absorbed and so missing from the continuum.

As GCT says, there is a further complication with Sodium the D line at 589nm is actaully two lines very close together because there are two energy states of the electron that are almost the same.