Class 4, 1/18/05
We discussed the material covered in the following reading material and HW3.
   · P.56-85  of  TB1:     Chpt 3, The Science of Astronomy;. 
   · P.114-128  of  TB1: Chpt 4 of  TB1, A Universe of Matter and Energy .

* Our universe is dynamic, democratic, and efficient .
* First Law of Thermodynamics: Conservation of Energy (Energy is conserved.)
* Energy is an important quantity. It's unit is joule = kg (m/s)^2 . Highlight it on p. A-2.
*  It is manifested in many forms: kinetic energy, potential energy, radiation energy (energy of light, which includes heat from objects with temperature). We discussed example of these energies, and how they change into different forms.
    (Food and heat energy are more commonly described in units of calorie = 4.2 joules, originally defined as the quantity of heat required to raise the temperature of 1 g of pure water by 1º C.)
* Rest mass energy E_0 = m_0 c^2. The Sun's energy is generated mainly by converting rest mass energy to radiation and kinetic energy.
* Hydrogen atom is made of one proton and one electron. The energy levels of the electron in hydrogen is discrete (like the elevator levels).
* The levels should be labeled as given in HW3, SA3.3; not like Fig. 4.11 on p.125 (or the figure in Problem 19, p.127) of TB1.
* When the electron in the hydrogen jumps from one of the exited levels to a lower level, it emits a photon (light particle).
* These distinct lights from the hydrogen carries the info about the part and era of the universe they are from. We will learn about them more later.
* Discussed unit of volume, liter.
* Related the above discussions to HW3, SA3.1, SA3.2, and SA3.3.

Discussion Session 2. 1/18/05
We discussed the material covered in the following reading material and HW3.
   · p.23 - p.52 of TB2,  Chpt 2, Space, Time, and the Eye of the Beholder;
* Time dilation: A moving clock, in any direction, always runs slower to the observer at rest with an identically made clock.
* Length contraction: The length of an object in the direction of its motion always looks shorter to the observer at rest with an identically made object.

Important announcements:
* There is no 10B-2. So, Chau's office hour is moved up to Tu 7-8pm, and all HW's will be due by 8pm, Tuesdays.
* Students unanimously favored to have three quizzes, with the worst one discounted.
So Every student's worst score of the quizzes are to be discarded, just as worst score of HWs. If a student misses a HW or a quiz, the student uses up this option. Best is not to miss any HW or quiz. If you miss one, try to do it yourself -- not just to look at the solutions, so your brain gets the exercise. You will need that practice and experience for the final exam. (Other policies about HWs and Exams stays the same as  stated in the Syllabus before and now.)

These changes have been made in the Syllabus. Please see the corresponding minor changes in the percentage weights of HW, Quizzes, and Final. Also, errors of quiz dates given in the Syllabus are corrected.