29. one point, from Lecture 29, a group question, short explanations

(a) .3 How Small? Each of you pull out a hair and very carefully measure it's thickness (NOT LENGTH!) on a ruler with millimeter markings. I will bring such a ruler to discussion, in case you don't have one. Choose the smallest one in your group. Write in scientific notation, that is, 10^(-something), how small that hair is. (.1) Approximately how many atoms would fit close-packed across that hair? (.1) How many nuclei would fit across the hair (if they were packed next to each other)? (.1)

(b) .3 Seeing Atoms. Three ways to ``see'' that atoms exist are Brownian Motion, Kinetic Theory, and a Scanning Tunneling Microscope (STM), which won a recent Nobel Prize. Describe how each of these gives convincing evidence for atoms. As you are answering this, say if any of the ways makes use of spectroscopy or scattering. (.1 apiece) If you are interested in seeing an STM up close, there's one in a lab under 1300 Sterling. Ask me. I show one in a later TV lecture.

(c) .4 Seeing Electrons. Explain how J. J. Thomson concluded that the electron's mass is 1/2000 the mass of a proton, instead of its charge being 2000 times the charge of a proton. You must describe two pieces of evidence. As you are answering this, say if any of the ways makes use of spectroscopy or scattering. (.2 apiece) There is some choice in what you select.

30. one point, from Lectures 29 and 30, plus a bit from Unit 2, a group question, short answers

(a) .4 Role of Electromagnetic Force in the Atom. Describe what the electromagnetic does in an atom. (.1) How does the electromagnetic force cause the ``death spiral'' (say what that is) of an electron in classical physics? (.1) What role does the electromagnetic force play in Rutherford scattering (say what that is). (.2) Hint: Many people erroneously think the nuclear force holds the atom together.

(b) .4 Planck's and Einstein's Insights into Light. How did Planck use h in the explanation of the spectrum of ``blackbody radiation'' (say what that is)? How did Einstein use h in the definition of a photon (say what that is)? (.2 apiece)

(c) .2 Light. What key role did light play in special relativity? (.1) How do we use light to understand atoms? (.1)

31. one point, from Lectures 31 and 32, short answers and one energy diagram which takes time

(a) .2 Spectra. Draw and label the discrete hydrogen spectrum. (.1) Draw and label a continuous spectrum at two temperatures, such as for tungsten. (.1) Label the axes, the colors, and draw the lines carefully, with labels where appropriate. You must have each spectrum correct to get credit for it.

(b) .2 Einstein's Photoelectric Effect (Nobel Prize 1921). What type of light can release electrons from matter? (.1) How many photons does it take to release an electron? (.1)

(c) .3 Photoelectric Energy Diagram. Draw a (labeled) simple graph of E versus f for the freed electrons. (.2) Indicate on the diagram the kinetic energy of the electron. (.1) Note I am not asking you for the whole photoelectric diagram and will deduct .2 if you draw it.

(d) .3 Action A. What is action A in classical physics (.1), how is it related to Planck's constant h (.1), and how did it enter Bohr's theory of the hydrogen atom? (.1)

32. one point, from Lectures 32 and 33, tall and time-consuming energy diagram and short calculations

(a) .7 Hydrogen Energy Diagram. Draw ACCURATELY the energy diagram for the hydrogen atom, allowing lots of space to label almost everything: the axes and numbers of the energy levels (.1); the values of the energy levels for n=1, 2, 3, 4, 5 (.1); the values of the energy given off as photons when the atom makes a transition from the 1st through 4th excited states to the ground state (.1); and the photon energies E_(5->2), E_(4->2), and E_(3->2) of the three colors we saw as the Balmer series (.1). Say which transition corresponds to which color in the Balmer spectrum (.1). Indicate on your diagram the energy of the photon required to set a ground-state electron free (.1). What type of photon is it (infrared, visible, ultraviolet) (.1)?

(b) .3 DeBroglie Wavelengths. Using h=6.63X10^(-34)kg-m² /s, calculate three deBroglie wavelengths: 1. Your own. Use your own mass in kilograms, and your fastest speed (estimate this, if you haven't measured it). (.1) 2. The deBroglie wavelength of an electron e with the following values of mass and velocity, m_e=10^(-30)kg, v_e=10^7m/s. (.1) 3. The deBroglie wavelength of a neutron n with m_n=10^-27kg, v_n=10^4m/s. (.1) You must show your work and have the right answer to get credit.

33. one point, from Lectures 33 and 34, many short answer, with some symbols

(a) .2 Neutron Diffraction (Nobel Prize 1994). The 1994 Nobel Prize in Physics was given for neutron diffraction research. Why would physicists use neutron instead of light (.1) or electron waves (.1) to probe the structure of matter?

(b) .2 Schrödinger's Psi. Define Psi (vecx,t) (.1) and |Psi (vecx,t)|^2 (.1). Here vec means vector.

(c) .2 Quantum Duality. Illustrate the meaning of ``wave-particle duality'' by saying what it has to do with light (.1) and the electron (.1).

(d) .1 Heisenberg's Uncertainty Principle. State Heisenberg's Uncertainty Relation for energy and time, defining each symbol, and say in your own words what this specific uncertainty relation means (.1).

(e) .3 Determinism. Express Newton's view of a deterministic physical world in terms of his second law and initial conditions for solving it (.1). How does the quantum theory of measurement destroy that view (.1)? When is Newton's description valid (.1)?

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