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20 Nov 2019

Suppose we have reason to suspect that a certain quantum objecthasonly three quantum states. When we excite a collection ofsuchobjects we observe that they emit electromagnetic radiationofthree different energies: 0.9 eV (infrared), 1.9 eV (visible),and 2.8 eV (visible).

(a) Draw a possible energy-level diagram for one of thequantumobjects, which has three bound states. On the diagram,indicate thetransitions corresponding to the emitted photons, andcheck thatthe possible transitions produce the observed photons andnoothers. When you are sure that your energy-level diagramisconsistent with the observed photon energies, enter the energiesofeach level (K+U, which is negative). EnterALLlevels before submitting; all of the energies must be correctto beproperly scored. The energy K+U of theground state is -4eV.
eV = energy of highest level(2nd excited state)
eV = energy of next highestlevel (1st excited state)
-4 eV = energy of groundstate

(b) The material is now cooled down to a very low temperature,andthe photon detector stops detecting photon emissions. Next abeamof light with a continuous range of energies from infraredthroughultraviolet shines on the material, and the photondetectorobserves the beam of light after it passes through thematerial.What photon energies in this beam of light are observed tobesignificantly reduced in intensity ("dark absorptionlines")?
Energy of highest-energy dark line: eV
Energy of lowest-energy dark line: eV

(c) There exists another possible set of energy levels fortheseobjects which produces the same photon emission spectrum. Onanalternative energy-level diagram, different from the one you drew inpart(a), indicate the transitions corresponding to theemittedphotons, and check that the possible transitions producetheobserved photons and no others. When you are sure thatyouralternative energy-level diagram is consistent with theobservedphoton energies, enter the energies of each level(K+U,which is negative). Enter ALL levelsbeforesubmitting; all of the energies must be correct to beproperlyscored.
eV = energy of highest level(2nd excited state)
eV = energy of next highestlevel (1st excited state)
-4 eV = energy of groundstate

(d) For your second proposed energy-level scheme, whatphotonenergies would be observed to be significantly reduced inintensityin an absorption experiment ("dark absorption lines")?(Given thedifferences from part (b), you can see that anabsorptionmeasurement can be used to tell which of your twoenergy-levelschemes is correct.)
Energy of highest-energy dark line: eV
Energy of lowest-energy dark line: eV

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Bunny Greenfelder
Bunny GreenfelderLv2
3 Sep 2019
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