34. one point, from Lecture 35, short explanations

(a) .4 Superconductivity. What two electromagnetic properties change as a superconductor goes through its critical temperature? (.2)
How might these two properties be useful to us? (.2)

(b) .4 Low T_c Superconductivity. What are a Cooper Pair (.1), an energy gap (.1), what do bosons have to do with them (.1), and how are these two quantum mechanisms related by the Bardeen/Cooper/Schrieffer theory (1972 Nobel) to the electrical conductivity (.1)?

(c) .2 High T_c Superconductivity. Give two features (.1 each) which are different about a high T_c superconductor from a low T_c superconductor.

35. one point, from Lectures 36, 37, and 38, a group question, short answers, no pictures necessary

(a) .3 Ozone and Greenhouse Effect. Why is the ozone layer necessary to us (.1)? Why is the greenhouse effect normally desirable (.1)? Discuss what is currently threatening both effects (.1). NOTE: The term "Greenhouse Effect" is usually used to mean the bad effect of too much greenhouse effect. I wanted you to realize we need the overall greenhouse effect.

(b) .2 Uncertainty Relations. What role does the energy-time uncertainty relation play in tunneling (used by Binnig and Rohrer, 1986 Nobel) (.1)? HINT: This really comes Lecture 34 earlier in the unit. The Scanning Tunneling Microscope and several other devices use tunneling, so I want you to understand why it's allowed. What role does the energy-time uncertainty relation play in choosing an element for an atomic clock (used by Ramsay, 1989 Nobel) (.1)?

(c) .3 Conductivity. What are energy bands in solids (.1), and why are they there (.1)? What does an energy gap have to do with electrical conductivity (.1)?

(d) .2 Computer Code. What is the logic of computer code called (.1)? How does the flow of electric current at a tiny scale implement this logic (.1)?

36. one point, from Lectures 36, 37, and 38, energy and other diagrams associated with Nobel prizes

(a) .3 Cascade Energy Process. Carefully draw and label the energy diagram for the energy cascade process common to the ozone effect and the greenhouse effect. Explain beside your diagram how that process describes each effect (Rowland, Molina, and Crutzen, 1995 Chemistry Nobel). (.1 each for diagram and two explanations)

(b) .2 Laser Energy Processes. Carefully draw and label the energy diagrams for population inversion (.1) and stimulated emission (.1) in lasers (Townes, Basov, and Prokhorov, 1964 Nobel). You may leave the two diagrams separate or merge them.

(c) .4 Conductivity Energy Processes. Carefully draw and label the energy diagrams for either kind of electrical conductor (.1), an insulator (.1), and both kinds (.2) of ``doped'' semiconductor.

(d) .1 P-N Junction Diagram. Carefully draw and label a diagram of a p-n junction, indicating how it can be a tiny capacitor ( Bardeen, Brattain, and Shockley, 1956 Nobel). The description in words is in my supplementary notes, but not the diagram. You can use your own lecture notes or draw the picture from the description.

37. one point, about a new subject but you can figure it out from earlier material in Unit 3, plus some material from Lectures 35 and 37, a group question, not easy but doable

The 1997 Nobel Prize. The 1997 Nobel Prize in Physics was awarded in October to Stephen Chu of Stanford University, Claude Cohen-Tannoudji of the École Normale Supérieure in Paris, and William Phillips ofthe National Institute of Standards and Technology in Gaithersburg, Maryland. The award (of about a million dollars) was for cooling atoms to 10s of millionths of a degree (Kelvin) above absolute zero (called microkelvins) and for trapping atoms with laser light.

(a) .4 Cooling. Use what you know about kinetic theory (.2), the dual nature of light(.1), and collisions (.1) to say how laser beams can cool atoms. HINT: Take this step by step as suggested by the phrasing of the question. The part of kinetic theory you need is in my answer to the HW3A question 29b on kinetic theory. The "collisions" I refer to are Unit 1-type collisions between particles, like the bike-car headon collision in the second homework set. What all gets transferred in such a collision?

(b) .4 Trapping. Use what you know about the dual nature of light (.2) and about collisions (.2) to say how laser beams can trap atoms. HINT: This follows straight from part (a).

(c) .2 Atomic Clock. One application of this work is more precise atomic clocks; in France there is now a clock accurate to a few parts in 10^15. What about this work makes a more accurate atomic clock? (.2)

38. one point, from Lecture 39, one diagram and short explanations

(a) .4 Feynman Diagram. Draw the Feynman diagram for two electrons approaching each other and exchanging a virtual photon (.1), and give the rules for external lines (.1), internal lines (.1), and vertices (.1).

(b) .2 Virtual Particle. How does the Uncertainty Principle allow the existence of a virtual particle (.1)? What do a photon and a virtual particle have in common (.1)? HINT: Think of definitions of a photon and a virtual particle.

(c) .2 Newton Lives! What are the two key differences (.1 apiece) between the new quantum rule for force in quantum electrodynamics (QED) and Newton's Second Law (in the form of change of momentum over time)?

(d) .2 Electric Charge. State the new role for electric charge in QED (.1) in a way which makes it clear that this is just a quantum version of the classical role for charge (.1).

39. one point, from Lectures 40 and 41, many short answers, with some symbols

(a) .2 Comparing Quarks and Leptons. What two properties do quarks and leptons have in common (.1)? What three properties of quarks make them way different from leptons (.1)?

(b) .2 Building a Baryon and Meson. Write a quark combination which is a legal electrically negative baryon, which is not an antiproton (.1). Write a quark combination which is a legal negative meson, which is not a pion (.1). These have to be completely correct: don't forget overlines, subscripts, and fractional charge!

(c) .2 Comparing Fermions and Bosons. What are two major differences (.1 apiece) between fundamental fermions and gauge bosons?

(d) .4 Comparing Interactions. Each fundamental interaction is distinctly different from the other three in some way/s. What are four things (.1 apiece) that are different about the electroweak? On the exam I will expect you to be able to answer what features are different about each of the four interactions, so study the chart in the Lecture 41 materials.

40. one point, from Lecture 42, many short answers, with some symbols

(a) .2 Standard Model. What is the ``Standard Model'' of particle theory (.2)?

(b) .2 High Energy Physics. What do we mean by the phrase high energy is short distance (.1)? Short distance is early times (.1)?

(c) .3 GUTs. What do we mean by the acronym ``GUTs'' (.1)? What is the GUTs scale of size (.1)? What physics is predicted to happen at the GUTs scale (.1)?

(d) .3 Symmetry Breaking. What is meant by a force having a symmetry (.1)? What is meant by symmetry breaking (.1)? What is meant by phase transitions in the early universe (.1)?

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