Video Transcript
What type of spectrum is shown
below? An emission spectrum, an absorption
spectrum.
This spectrum referred to is this
one, and we can see that it consists of bright lines, separated by dark regions. The bright regions represent the
observed wavelengths of light, and the dark regions represent the wavelengths of
light where we do not observe anything. Now, we can recall that spectra
like the one shown in our figure result from electrons transitioning between various
energy levels in an atom or molecule.
Because the energy levels in an
atom or molecule are discrete and the differences in energy between levels are
discrete, an atom or molecule will only emit and absorb light at very specific
wavelengths. Looking back at the picture, we see
that the bright lines representing light that we observe only occur at very specific
discrete wavelengths. In other words, the light that we
observe is only at discrete wavelengths.
Now, remember our two possibilities
are that discrete wavelengths are absorbed or discrete wavelengths are emitted. Now, because we are observing light
at these discrete wavelengths, this light cannot be light that was absorbed by the
atom or molecule. Rather this is light that was
emitted by the atom or molecule. That’s why we can see it.
So, the notable features of the
spectrum are emitted light, and it is therefore an emission spectrum. This is choice (A).
Choice (B) an absorption spectrum
would have notable features, being the absorption of light. And so instead of seeing bright
lines with dark regions in between, we would see bright regions in between several
dark lines that corresponded to the wavelengths of light that an atom or molecule
absorbed. However, those dark lines would be
in the same places as the bright lines of the emission spectrum, because atoms and
molecules absorb and emit light at the same wavelengths.
