Physics I Announcements Quiz review Superconductivity last topic of Chap 42 Going nuclear Chap 43 How the sun shines 1 Who is this handsome man Final Exam Overview Final exam 6 problems 2 pages of conceptualshort answer questions up to Chap 44 ID: 1024483
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1. Superconductivity+Nuclear Physics IAnnouncementsQuiz (review)Superconductivity (last topic of Chap 42)Going nuclear ! (Chap 43)How the sun shines1Who is this handsome man ?
2. Final Exam OverviewFinal exam: 6 problems + 2 pages of conceptual/short answer questions (up to Chap 44).Problem 1: Interference/DiffractionProblem 2: Heisenberg Uncertainty Principle (Particles and/or Waves)Problem 3: QM I: Wave FunctionsProblem 4: QM II: Atomic StructureProblem 5: Molecules/Solid StateProblem 6: Nuclear PhysicsProblems 7&8: Short answer questions (will include energy/momentum special relativity)2Date: Monday, December 11th, 12:00-14:00
3. https://www.hawaii.edu/ecafe/The ECAFE course evaluation system is now open. Please evaluate PHYS274 for this semester.
4. What planet is this ?What is the main component of its atmosphere ?Ans: CO2The temperature of the surface of Venus is 7350 K = 8630 FVibrational modes are key (tri-atomic)
5. Q36.1As the temperature increases, more electrons areFound below the Fermi energyExcited above the Fermi energyFound in the conduction band of metalsInsulators become superconductors5
6. Q36.1As the temperature increases, more electrons areFound below the Fermi energyExcited above the Fermi energyFound in the conduction band of metalsInsulators become superconductors6
7. Does this energy band picture depicts a n-type or p-type or an intrinsic semiconductor?N-typeP-typeIntrinsicExtrinsic7Q36.2
8. Does this energy band picture depicts a n-type or p-type or an intrinsic semiconductor?N-typeP-typeIntrinsicExtrinsic8Q36.2Note:“Intrinsic semiconductors” are un-doped semi-conductors. “Extrinsic semi-conductors” are semi-conductors after being doped.
9. This picture denotes a Germanium (group IV) semiconductor is doped with a Gallium (group III) impurity. What type of semiconductor is this ?N-typeP-typeN-P-N typeP-N-P type9Q36.3
10. This picture denotes a Germanium (group IV) semiconductor is doped with a Gallium (group III) impurity. What type of semiconductor is this ?N-typeP-typeN-P-N typeP-N-P type10Q36.3The hole in red is free to roam about the atomBTW: Using the Hall effect (PHYS170), one can verify that holes are charge carriers in the p-type and electrons in the n-type
11. Does this energy band picture depict a n-type or p-type or an intrinsic semiconductor?N-typeP-typeIntrinsicExtrinsic11Q36.4
12. Does this energy band picture depict a n-type or p-type or an intrinsic semiconductor?N-typeP-typeIntrinsicExtrinsic12Q36.4Electron goes to the acceptor level and leaves a hole in the valence band
13. A. n-p semiconductor sandwichB. p-n semiconductor sandwichC. p-n-p or n-p-n semiconductor sandwichD. Large scale integrated circuitE. A (p p p) or (n n n) semi conductor sandwich with different impurity dopings.A transistor is a13Q36.5
14. A. n-p semiconductor sandwichB. p-n semiconductor sandwichC. p-n-p or n-p-n semiconductor sandwichD. Large scale integrated circuitE. A (p p p) or (n n n) semi conductor sandwich with different impurity dopings.A transistor is a14Q36.5
15. Superconductivity refers toA. An increase in resistivity at low temperaturesB. Small decrease in resistivity at low temperaturesC. The absence of resistance below a critical temperature.D. The absence of conductivity above a critical temperature.15Q36.6
16. Superconductivity refers toA. An increase in resistivity at low temperaturesB. Small decrease in resistivity at low temperaturesC. The absence of resistance below a critical temperature.D. The absence of conductivity above a critical temperature.16Q36.6
17. Superconductivity17
18. SuperconductivityDemoTemperatureResistivityZero!The BCS physics in a nutshell:At low temperatures, the electrons in superconductors bind into pairs that have zero spin – the pairs are “composite bosons.” They love being in the same state and they condense into it. A boson condensate can flow without scattering, it’s a charged “superfluid.”Meanwhile a gap (not a band gap) opens up and there are no single-electron states left to accelerate and experience scattering. Zero Resistance!This does not happenin a superconductor.Bardeen, Cooper and Schrieffer explained all this in 195618
19. 1972 Nobel Prize in Physics 19
20. High Tc superconductorsDo not need liquid helium, huge cost savings but brittle and hard to handle.But the BCS mechanism does not explain these materials (need magnetic spin interactions between electron pairs)Liquid nitrogen20
21. Some Applications of SuperconductivityTo date, applications have mostly been specialized. In particular, it is much cheaper to operate high field (high current) electromagnets if the wire is superconducting.MRI (Magnetic Resonance Imaging)or NMR (Nuclear Magnetic Resonance)LHC (Large Hadron Collider)Accelerator in Geneva, Switzerland21For example, Queen’s Hospital
22. Some Applications of SuperconductivitySuperconducting Quantum Interference Devices (SQUIDs)are also used to make verysensitive magnetic fieldmeasurements (e.g., to makeone part in 1012 measurements ofmagnetic susceptibility).http://rich.phekda.org/squid/technical/part4.htmlCan use superconducting junctions for quantum computing,the next frontier.22Being added to UH course PHYS481L
23. More Applications of SuperconductivitySuperconducting magnets on a train above a track made out of a permanent magnet lock the train into its lateral position. It can move linearly along the track, but not off the track.Shanghai airport magnetic levitation train (431 km/h or 268 mph)A project is underway to build a similar train from Tokyo to Nagoya.(Current travel time 1h 40 min)23
24. More Applications of SuperconductivityThe holy grail of SCtechnology is electrical power distribution (7% is lost in the power grid). This is one reason why HiTc superconductors are important, but it’s not yet competitive.http://www.nano-opt.jp/en/superconductor.htmlCommercial superconducting power cable24
25. Goals for Chapter 43To understand some key properties of nucleiTo see how nuclear binding energy depends on the number of protons and neutronsTo investigate radioactive decayTo learn about hazards and medical uses of radiationTo analyze nuclear reactionsTo investigate nuclear fissionTo understand the nuclear reactions in our sun 25
26. A few important points about nuclear physicsHow can we date ancient biological artifacts? Most of the mass of an atom is found in its tiny nucleus.Some nuclei are stable, but others spontaneously decay.Fission and fusion are important nuclear reactions. We (life on earth) would not exist without the fusion in our sun.26
27. Properties of nucleiThe nucleon number A is the total number of protons and neutrons in the nucleus. The radius of most nuclei is given by R = R0A1/3 where R0=1.2 x 10-15m=1.2 fmAll nuclei have approximately the same density.For example, the most common kind of iron nucleus has A=56. What is its radius, approximate mass and density ?27
28. Iron nucleusFor example, the most common kind of iron nucleus has A=56. What is its radius, approximate mass and density ? (Note 1 amu = 1.66 x 10-27kg).Question: But the density of solid iron is about 7000 kg/m3 this is orders of magnitude more. What holds the nucleus together ?28
29. Iron nucleus cont’dFor example, the most common kind of iron nucleus has A=56. What is its radius, approximate mass and density ? (Note 1 amu = 1.66 x 10-27kg).But the density of solid iron is about 7000 kg/m3 this is orders of magnitude more. What holds it together ?Ans: Strong interaction or strong nuclear forceInteresting to note that neutron stars are macroscopic objects with density of nuclei.29Recently neutron stars have been in the news. Why ?
30. Aug 17, 2017 LIGO followed by X-ray and optical telescopes, detected a neutron star merger event
31. The nuclear forceThe nuclear force binds protons and neutrons together. It is an example of the strong interaction.Important characteristics of the nuclear force:It does not depend on charge. Protons and neutrons are bound. It has a short range, of the order of nuclear dimensions.Because of its short range, a nucleon only interacts with those in its immediate vicinity.It favors binding of pairs of protons or neutrons with opposite spins and with pairs of pairs (a pair of protons and a pair of neutrons, each pair having opposite spins). 31
32. Nuclides and isotopesThe atomic number Z is the number of protons in the nucleus. The neutron number N is the number of neutrons in the nucleus. Therefore A = Z + N.A nuclide is a single nuclear species having specific values for both Z and N.The isotopes of an element have different numbers of neutrons.Question: These are three isotopes of hydrogen. How many protons and neutrons do they contain ? What are they called ?32
33. Nuclides and isotopes cont’dQuestion: These are three isotopes of hydrogen. How many protons and neutrons do they contain ? What are they called ?Ans: 1proton, 1 proton and 1 neutron, 1 proton and 2 neutrons.They are called hydrogen, deuterium, and tritium. Follow-up: What happens if hydrogen is replaced by deuterium in water ?33
34. Nuclides and isotopes cont’dLife and death question: What are the two isotopes of the element uranium ?Ans: U235 (92 protons and 143 neutrons) and U238 (92 protons and 146 neutrons). The values are the atomic numbers of the elements. Question: Which one is useful for atomic energy and bombs ? Which one is more common ?Ans: 235U with low enrichment for nuclear power plants, high enrichment for bombs. U238 is much more common.34
35. Nuclides and isotopes cont’dLife and death question: What are the two isotopes of the element uranium ?President Mahmoud Ahmadinejad of Iran touring centrifuges for isotope enrichment.35