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Chapter 8: Energy Quantization

Matter & Interactions
Pages: 323 - 348

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26 Questions for Chapter 8: Energy Quantization

  1. The mean lifetime of a certain excited atomic state is 5 ns. What is the probability of the atom staying in this excited state for t=10 ns or more?

    Found on Page 344
  2. At t =0 all of the atoms in a collection of 10000 atoms are in a excited state whose lifetime is 25 ns. Approximately how many atoms will still be in excited state at t= 12 ns.

    Found on Page 344
  3. N=1 is the lowest electronic energy state for a hydrogen atom. (a) If a hydrogen atom is in a state N=4, what is K+U for this atom (in eV)? (b) The hydrogen atom makes a transition to state N=2, Now what is K+U in electron volts for this atom? (c) What is energy (in eV) of the photon emitted in the transition from level N=4 to N=2? (d) Which of the arrows in figure 8.40 represents this transition?

    Found on Page 344
  4. The Frank Hertz experiment involved shooting electrons into a low density gas of mercury atoms and observing discrete amounts of kinetic energy loss by the electrons. Suppose that instead the similar experiment is done with a very cold gas of atomic hydrogen, so that all of the hydrogen atoms are initially in ground state. If the kinetic energy of an electron is 11.6 eV just before it collides with a hydrogen atom. How much kinetic energy will the electron have just after it collides with and excites the hydrogen atom?

    Found on Page 344
  5. Suppose we have reason to suspect that a certain quantum object has only three quantum states. When we excite such an object we observe that it emits electromagnetic radiation of three different energies: 2.48eV(green), 1.91eV(orange), and 0.57eV(infrared). (a) Propose two possible energy-level schemes for this system. (b) Explain how to use an absorption measurement to distinguish between the two proposed schemes

    Found on Page 344
  6. Found on Page 344
  7. Energy graphs: (a) Figure 8.41 shows a graph of potential energy vs. interatomic distance for a particular molecule. What is the direction of the associated force at location A? At location B? At location C? Rank the magnitude of the force at locations A,B and C. (That is, which is greatest , which is smallest, and are any of these equal to each other?) For the energy level shown on the graph, draw a line whose height is the kinetic energy when the system is at location D.

    Found on Page 345
  8. A bottle contains a gas with atoms whose lowest four energy levels are -12eV, -6eV, -3eV, and -2eV. Electrons run through the bottle and excite the atoms so that at all times there are large numbers of atoms in each of these four energy levels, but there are no atoms in higher energy levels. List the energies of the photons that will be emitted by the gas.

    Found on Page 345
  9. The photon energy for green light lies between the values for red and violet light. What is the approximate energy of the photons in green light? The intensity of sunlight above the Earth’s atmosphere is about 1400 W (J/s) per square meter. That is, when sunlight hits perpendicular to a square meter of area, about 1400 W of energy can be absorbed. Using the photon energy of green light, about how many photons per second strike an area of one square meter? (This is why the lumpiness of light was not noticed for so long.)

    Found on Page 324
  10. Match the description of a process with the corresponding arrow in figure 8.38: (a) Absorption of a photon whose energy is E1-E0. (b) Absorption from an excited state (a rare event at ordinary temperatures). (c) Emission of a photon whose energy isE3-E1 . (d) Emission of a photon whose energy isE2-E0 . (e) In drawing arrows to represent energy transitions, which of the following statement are correct. (1) it doesn’t matter in which direction you draw the arrow as long as it connects the initial and final states. (2) For emission, the arrow points down. (3) For absorption, the arrow points up. (4) The tail of the arrow is drawn on the initial state. (5) The head of the arrow is drawn on the final state. (6) It is not necessary to draw and arrowhead.

    Found on Page 343

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