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# How do I solve this light/energy problem?

In the investigation of the electronic absorption spectrum of a particular element, it is found that a photon having a wavelength  of 500nm provides just enough energy to promote an electron from the second quantum level to the third. From this information, we can deduce:

A. The energy of the n=2 level
B. The energy of the n=3 level
C. The sum of the energies of n=2 and n=3
D. The difference in the energies between n=2 and n=3
E. All of the above

### 2 Answers by Expert Tutors

Philip P. | Effective and Affordable Math TutorEffective and Affordable Math Tutor
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Let:
• Ep = the energy of the photon = hc/λ  This quantity is known)
• E2 = the energy of level n=2
• E3 = the energy of level n=3

A.  Knowing Ep tells us nothing about E2
B.  All we know about E3 is that E3 = E2 + Ep, but we still don't know E2
C.  E2 + E3 = E2 + E2 + Ep = 2E2 + Ep.  Still don't know E2
D.  E3 - E2 = E2 + Ep - E2 = Ep = hc/λ.  Aha, we know Ep so we know the difference in energy between E2 and E3.
E.  Don't know E2 or E3