When Examined with a Grating Spectrograph,the Discharge from Helium Gas

question 16

Multiple Choice

When examined with a grating spectrograph,the discharge from helium gas has bright radiation at a relatively few discrete wavelengths; the discharge from nitrogen gas has radiation in bands with a very large number of discrete wavelengths.What is the reason for this difference in the spectra of these two gases?

• A)The atoms of the helium gas have two electrons whereas the atoms of the nitrogen gas have many electrons; therefore,the nitrogen gas gives a more complicated spectrum.
• B)The nitrogen gas has molecules that have rotational and vibrational energies that produce bands of closely spaced wavelengths in the spectrum.
• C)The nitrogen gas discharge is hotter,which "smears out" the wavelengths of the radiation according to Planck's law for blackbody radiation.
• D)The levels of the helium atoms can be obtained from the Bohr theory of atoms,which gives a few relatively discrete allowed energies,whereas nitrogen must be described by the band theory,which gives continuous bands of allowed energies.
• E)None of these is correct.

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