Exam 2

• The exam will consist of 50 multiple choice questions.
• Exam 2 covers Lectures 10-17.
• You need a No. 2 pencil and an eraser.
• You are not allowed to use a calculator.
• Enter your name and your ID number.
• Turn in the answers and leave whenever you are done.
• "Re-take" option
• strictly optional
• likely to help but it can hurt your grade
• new grade = (75% original grade) + (25% "re-take" grade)
• take a new answer sheet and return it to my office (LGRT B522) by Noon next day
• no make-up exam (a reminder)

Exam 2 Preparation

The following is a list of things to review in preparation for the exam. It is roughly in the order of importance and relevance, so start from the top and work your way down as time permits. Look at items 8-10 if you have extra time, but don't start your study by reading the whole textbook!

1. Lecture outlines on web
2. In-class quizes
3. Sample exam questions are in OWL
4. OWL prelecture quizes and HWs 3 & 4
5. extra practice quizes
6. "Test Yourself" questions at the end of each Units in the textbook
7. Quantitative concepts you should know:
• parallax: compute a distance from a measured parallax
• inverse square law: many examples in the HW and inclass quizes.
• magnitude system: stars A & B with different magnitudes of brightness. Which one is brighter and by how much?
• Stefan-Boltzmann law: how does the luminosity of a star depend on the size and temperature?
• Kepler's law for binary stars: calculate mass for a pair of orbiting stars
• mass-luminosity and mass-(main sequence)lifetime relation: Stars A & B have different mass. How do their luminosity compare? Which star lives longer and by how much?
• ideal (perfect) gas law: how are pressure, density, volume, and temperature related?
• black hole (Schwarzschild) radius: how does the size of a BH depend on its mass?
• Keg's Law (for practicing ratios)
8. "Review Problems" at the end of each chapter
9. Know what the bold-faced terms mean in the textbook
10. No need to memorize physical constants

Q & A session: April 9 (Wednesday) at 5pm in HAS 134

Answers to inclass quizes 10-17

• quiz 10: A (answer=4; heat conduction rate varies with different material); B (answer=4)
• quiz 11: A (answer=3; see the answer on the question page); B (answer=2); C (answer=5)
• quiz 12: A (answer=4); B (answer=3); C (answer=4; distance = 1/p)
• quiz 13: A (answer=2; M=10³/30²=1000/900=1.1 solar mass); B (answer=4; luminosity increases as square of size and the 4th power of temperature, so 100²/2⁴=10000/16=625 times larger in luminosity.); C (answer=3; same color means same temperature, and more luminosity means larger in size); D (answer=1; see the lecture note)
• quiz 14: A (answer=2; hot oven still emits infrared light, which you can sense as heat.); B (Part 1: 30x10=300 miles for the Cooper and 0.6x100=60 miles for M1A1, so answer=2. Part 2: The more massive star has stronger gravity and thus higher temperature in the core, which promotes a much higher fusion rate. Only 10 times more mass, so the fuel is used up much more quickly, leading to a shorter life.); C (answer=4; The Sun will become a white dwarf but will not explode as a supernova)
• quiz 15: A (answer=3; Ford Explorer is about 100 inches in length, so it will be about 1 inch long when compressed by a factor of 100); B (answer=2; the WD will shrink because gravity increases but the pressure supporting it does not); C (answer=4; all WD supernova explode when their mass is 1.4 solar mass, and thus they all have about the same energy of explosion); D (answer=4; that's another factor of 100 smaller than a match box)
• quiz 16: A (answer=3; the monkey is hit by the bullet because both the monkey and the bullet are in free fall, affected identically by the pull of the Earth's gravity.); B (Part 1 answer=3 because 900+10=910; Part2 answer=4 because speed of light is the same for everyone); C (answer=4; this is the length contraction question, asking to solve for v/c where the square root of (1-(v/c)²) equal 1/2. Squaring both sides, you get 1-(v/c)² = 1/4, or (v/c)² = 3/4. So, v/c = (3/4)^1/2.); D (answer=3)
• quiz 17: A (answer=3); B (answer=4; 3/1,000,000 km = 3/1000 m = 3/10 cm = 3 mm, which is the size of an ant.); C (answer=3); D (answer=3 because mass is the same); E (answer=5. The Earth will continue to circle the black hole Sun since the mass did not change.)