Modern Physics unit test
A test on this unit alone, marked as a percentage and a letter grade — for the test your class is actually sitting, rather than for May. Answer everything, then submit once: seeing the answer to question 3 before attempting question 4 makes the final percentage meaningless.
What half-life is immune to
Photoelectric effect
Emission vs absorption spectra
Why the electronvolt exists
Binding energy conversion
Fission vs fusion
Binding energy PER NUCLEON is the meaningful figure
Radioactive decay is random
Photon energy
Photoelectric graph
Work function
Absorption versus emission spectra
Short answer 1. Define or explain: Counting halvings
3 ptsShort answer 2. Define or explain: Why fusion and fission both release energy
3 ptsShort answer 3. Define or explain: Photon momentum
3 ptsShort answer 4. Define or explain: Why atomic spectra are discrete
3 ptsFree response
12 ptsTRANSLATION BETWEEN REPRESENTATIONS (Question 2, 12 points). Figure 1 shows the energy levels of a hypothetical atom: n = 1 at −5E0, n = 2 at −3E0, and n = 3 at −2E0. For C–D: a device can emit monochromatic electromagnetic radiation whose wavelength λ can be varied continuously. Photons with wavelength λ0 have energy 4E0. (Figure 2 provides axes of photon energy E versus λ for λ0 < λ < 4λ0.)
A. Describe all possible atomic transitions on the Figure 1 diagram that could result in the emission of a photon (each as an arrow between states).
B. Derive an expression for the wavelength of the highest-energy photon that can be emitted from the atom, in terms of E0 and physical constants, as appropriate.
C. Describe the curve of emitted-photon energy E as a function of λ for λ0 < λ < 4λ0 on Figure 2, given that photons of wavelength λ0 have energy 4E0.
D. A student claims that, based on the energy states in Figure 1, the atom can emit a photon of wavelength λ0 and energy 4E0 like the device in part C. Indicate whether the claim is correct or incorrect, and briefly justify by referencing the representation in part A.