# HW 15-solutions - shusi(oos225 HW 15 turner(58465 This...

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shusi (oos225) – HW 15 – turner – (58465) 1 This print-out should have 20 questions. Multiple-choice questions may continue on the next column or page – find all choices before answering. 001 10.0points A certain laser outputs pure red light (photon energy 1 . 8 eV) with power 575 mW. How many photons per second does this laser emit? Consider just four of the energy levels in a certain atom, as shown in the diagram below. n = 2 n = 3 n = 4 Convert eV to Joules: 003(part1of3)10.0points Consider just four of the energy levels in a certain atom, as shown in the diagram below. n = 2 n = 3 n = 4
(1 . 8 eV) 1 . 6 × 10 - 19 J eV 2 . 88 × 10 - 19 J . Then, number of photons emitted per sec- ond is simply 0 . 575 W all possible transitions among these levels? Which transition corresponds to the highest- frequency light emitted? Which transition corresponds to the lowest-frequency? 002 10.0points Suppose we have reason to suspect that a cer- How many spectral lines will result from all possible transitions among these levels? Which transition corresponds to the highest- frequency light emitted? Which transition corresponds to the lowest-frequency?
tain quantum object has only three quantum states: E 0 , E 1 , and E 2 . When we excite such an object we observe that it emits electro- magnetic radiation of three different energies: 2 . 48 eV (green), 1 . 77 eV (orange), and 0 . 71 eV (infrared). If we now illuminate the (cooled) object with continuous radiation from 0 . 4 eV to 2 . 7 eV, we observe absorption at 0 . 71 eV and at 2 . 48 eV. From this data, what is the difference in energy between E 2 and E 1 ? 3. three; level 2 to level 1 transition; level 4 to level 3 transition. 4. three; level 4 to level 3 transition; level 2 to level 1 transition. Explanation:
The energy levels can be taken as E 0 = 0 E 1 = 0 . 71 eV E 2 = 2 . 48 eV . If the levels were E 0 = 0, E 1 = 1 . 77 eV, and E 2 = 2 . 48 eV, then we would observe absorption at 1 . 77 eV and 2 . 48 eV instead. n = 1 The highest-frequency transition is from quantum level 4 to level 1. The lowest- frequency transition is from quantum level
shusi (oos225) – HW 15 – turner – (58465) 2 4 to level 3. 004(part2of3)10.0points An electron de-excites from the fourth quan- tum level to the third and then directly to the ground state. Two photons are emitted. How does the sum of their frequencies com- pare to the frequency of the single photon that would be emitted by de-excitation from the fourth level directly to the ground state?
4. The sum is equal to the frequency of the single photon. correct 1. Because energies are additive, so are the
frequencies. However, the wavelength rela- tionship is not that simple: wavelength is in- versely proportional to the frequency, so the reciprocals of the wavelengths are additive: 1 λ 4 3 + 1 λ 3 1 = 1 λ 4 1 005(part3of3)10.0points