Q275 · Practice questionComplex familiar3 marks
QUESTION 275 (3 marks)
A gas initially has its electrons in the ground state. Its absorption spectrum has narrow lines at and . Candidate model X has levels , and ; model Y has levels , and . Assume only these levels and neglect recoil. Use .
a)[3 marks]
Determine which model is consistent with both absorption lines. Support your answer numerically.
WORKED SOLUTION
3 marksPractice marking scheme
ANSWER
(a) Model X; the photon energies are 4.00 eV and 2.00 eV.
Worked solution
(a) gives and . From the ground level, X allows both gaps, while Y allows 3.00 and 4.00 eV rather than 2.00 and 4.00 eV.
Equivalent physically justified methods, alternative valid sketches and consistent units accepted.
Accept sensible significant figures and consistent rounding from stated constants.
Part a: Calculate both photon energies.
Part a: Match both ground-state excitation gaps in X.
Part a: Reject Y because its 2.00 eV ground-state gap is absent.
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