Video Transcript
The figure below shows two spectra,
A and B. Does the 443-nanometer emission
line in spectrum A appear in spectrum B?
The two emission spectra we’re
asked about are these two here labeled A and B. And we know they’re emission
spectra because they consist of bright lines on a dark background. If they consisted of dark lines on
a bright background, we would know they were absorption spectra.
Now, we are asked if the
443-nanometer emission line, which appears in spectrum A here, also appears in
spectrum B. This is a useful question to ask
because all spectra from a particular type of atom or molecule are the same and all
spectra from different atoms or molecules are different.
So, by comparing spectra, we can
determine if there’re any atoms or molecules that are in the sample that was used to
prepare one of the spectra, but not in the sample that was used to prepare the
other. In this case, we see that the
443-nanometer line does not appear in spectrum B even though it does appear in
spectrum A. So the answer to our question is
no. The 443-nanometer line that appears
in spectrum A does not appear in spectrum B. And again, we can conclude from
this that there’s at least one atom or molecule, specifically the one with an
emission line at 443 nanometers, that was in the sample that was used to prepare
spectrum A and was not in the sample that was used to prepare spectrum B.
In fact, we could actually get very
close to identifying exactly the contents of the samples used to prepare these two
spectra by comparing them to known spectra from pure samples of atoms and
molecules.
