Class 14, 2/24/04;
Announcements:
1. Replies to "Questionnaires after Quiz 2" are confidential. If some
of the comments can benefit the whole class, an anonymous summary of them
will be made for the class.
2. A link "Hints to Homework 7" was made, near this class page link, just
in case some of you did not receive those e-mail communications about HW7.
Class Highlights
* We discussed the unit of angular momentum: xxx;
** Using the angular momentum of the
planets as an example.
** The unit of angular momentum is (the
unit of length) x (the unit of momentum).
* The Planck constant h-bar (h/2pi) has precisely the unit of angular
momentum; not only that,
* The Planck constant h-bar is the quantity that nature chooses
to use as the basic entity in terms of which the angular momentum of particles
can either be integers or half integers!
** Fermions: spin S = (1/2) h_bar, (3/2) h_bar, (5/2)
h_bar, etc.
*** Spin of electron,
S_electron = (1/2) h_bar; S_proton = (1/2) h_bar; S_neutron = (1/2) h_bar;
S_neutrino = (1/2) h_bar;
*** Spin of quarks,
S_quarks = (1/2) h_bar;
** Bosons (or mesons): spin S = 0 h_bar, 1 h_bar,
2 h_bar, etc.
*** Spin of
photon, electromagnetic force particle, S_gamma = 1 h_bar;
*** Spin of weak
force particles, S_Z = S_W = 1 h_bar;
*** Spin of
gluon, strong force particles, S_g_st = 1 h_bar;
*** Spin of graviton,
gravity force particle, S_g_Gr = 2 h_bar.
* Fermions do not want to share an energy/spin spot --- the Pauli
exclusion principle --- degeneracy pressure (that sustains stars by balancing
the pressure from gravity. We will learn about it in the next topic.)
* Charges of particles are also quantized in a unit which a proton
has, Q_p, which is also denoted by e as in eV, for electron volt.
** Charge of a proton, Q_p = 1 Q_p;
Charge of a neutron, Q_n = 0 Q_p;
** Charge of an electron, Q_p =
(- 1) Q_p; Charge of a neutrino, Q_neutrino = 0 Q_p; etc.,
* Every particle have their corresponding anti-particle, denoted
by a bar on the top of the letter that denotes the particle. An antiparticle
has the same mass and spin, but opposite charge, as the particle, e.g.,
** Charge of an anti-proton, Q_p_bar
= (-1) Q_p; Charge of an anti neutron, Q_n_bar = 0 Q_p;
* All neutral force particles are their own anti-particles; so,
anti-photon is a photon, etc.
* We demonstrated the picture of blocks of the experimentally established
basic particles, from which all the know matter are made from
** The up quark, u : S_u = (1/2) h_bar; Q_u = (2/3)
Q_p;
** The down quark, d : S_d = (1/2) h_bar; Q_d = (-1/3)
Q_p;
* To make the proton, a Fermion with charge 1 Q_p ,
the minimum number of quarks needed is three, and that is what nature has
chosen to make.
*** The proton
is made out two up quarks and one down quark, plus lots of gluons;
*** The anti-proton
is made out two anti-up-quarks and one anti-down-quark, plus lots of gluons.
* To make the neutron, a Fermion with charge 0 Q_p , the
minimum number of quarks needed is three, and that is what nature has chosen
to make.
*** The neutron
is made out of two down quarks and one up quark, plus lots of gluons;
*** The anti-neutron
is made out of two anti-down-quarks and one anti-up-quark, plus lots of gluons.
* From protons and neutrons, nuclei of atoms are made. Nuclei
plus the surrounding electrons, (electrically neutral) atoms are formed
: hydrogen, helium, etc; See the Periodic Table in TB 1; and, even better,
the link given in the course web, near to this class page.
* From atoms, molecules form: e.g., water molecule (two hydrogen
and one oxygen), etc.
* Totally there are three copies (families, or generations) of quark-pairs
and lepton-pairs:
** (up, down) quarks and (electron, electron-neutrino)
leptons;
** (charm, strang) quarks and (muon, muon-neutrino)
leptons;
** (top, botton) quarks and (tau, tau-neutrino) leptons.
* Ordinary matters we know are mostly made out of protons, neutrons,
electrons, which are from the first family, and force particles.
* The block view of matter was shown again.
************************* Below was posted before the class. *****************************
New Policies & Reminders
* Bonus points will be awarded to those who neatly lay out equations
on the blank back pages or separate sheets, not on the front pages, in
HWs and in Exams (in additional to being given partial credit considerations
if the final answer is incorrect, as announced before).
[Please see the three examples provided by Professor Chau for the Solution
to Quiz 1, if you have not done so. Many of you have been following the
guidelines and getting good results. However, still many more students
can improve performance by simply writing out equations neatly. It is obvious
that none of you want to write out sentences in a scattered around way. Equations
do talk, however, they have to be given a chance.]
[Also, it is interesting to note that both in recent HWs and in Quiz
3, statistically speaking, students are performing now equally well, if
not better, on problems involving equations or computations. It can not be
over emphasized that understanding (understanding, and understanding) is
the key for all learning and performance.]
* It should be clear by now, by Quiz 1 & 2, that students
will get most of the exams if they know and understand the answers to HWs.
Please remember to bring your questions on previous Quizzes and HWs to
the discussion sessions. (As always, you are welcome to ask Professor Chau
by e-mail.) As you all know, Quiz 3 will be held Thursday of next week,
3/4/04, and the Final Exam is only two weeks after that. Therefore, every
discussion may be considered as exam preparation session, in addition to
discussing the current HWs.
* Those who want to have a HW assignment before other students have it
(usually at the end of Thursday classes, including the one after Quiz 3)
needs to make a request to Professor Chau by sending her an e-mail before
Wednesday midnight. She will then confirm by replying to the e-mail.
A copy of the HW assignment and the e-mail communication will be put in
the tray in front of her office at about 1pm on Thursday. (Please
understand that it is very distracting to make requests right before her
lectures or during classes.)
* Those who attend the Thursday classes please make sure to pick up the
HW assignment, and please try not to misplace or lose it. Extra copies
of HW assignments will be made available in the tray and in the following
class during the sign-up period. A blue mark reminder will be put on those
copies so distributed.
* Please pick up graded HWs promptly at the end of Tuesday classes.
Any that are not picked up will be put in the tray in front of Professor
Chau's office, and a blue reminder mark will be put on the sign-up sheet.
(By the way, there are still many graded HWs not being picked up. They will
be distributed with the graded Quiz 2, so the tray will have a clean start
before the Tuesday class, 2/24/04. Please help to keep it clean.)
* As always, blue marks are reminders, not for scoring at all. However,
also as always, your cooperation and help are appreciated.
Preview of Lecture:
* We will finish discussing
TB1,
S4, Building Block of the Universe, and
TB2, Chapter
9, Experimental Signatures; Chapter 10: Quantum Geometry.
* Show and discuss Quiz 2 statistics
* Distribute graded Quiz 2, solutions, & statistics; and graded HW6
& solutions.
Sign-up items, Class
14, 2/24/04
(1) Have you received the e-mail "Questionnaires after Quiz 2" ?
Y, or N.
(2) Have you read the above New Policies & Reminder?
Y, or N.
(3) Have you finished reading the reading assignments
TB1, S4, Building Block of the Universe, and
TB2, Chapter
9, Experimental Signatures;
Chapter 10: Quantum Geometry.?
Y, P (partial),
or N.
(4) Initial.