Exam #2 Study Guide:

Exam 2 will have 40 multiple choice questions based on material covered in lectures from 9-27 to 10-27. Material from HW4-8 may be on the exam. A few of the questions will involve simple calculations, so you should bring your calculator. You will not need your clicker. You may bring one double-sided 8.5x11 inch sheet of paper with notes to the exam.

I Electricity and Magnetism

  1. Magnetic force: a compass has a north and a south magnetic pole. North poles are attracted to south poles; like poles repel.
  2. The Earth is like a big magnet with a south (north) magnetic pole near its North (South) geographic pole. All the planets and our Sun have magnetic fields.
  3. Electric force: like charges repel; opposite charges attract
  4. Charge is a property of matter. The fundamental unit is 1.6E-19C. This is the charge on a proton. An electron has a charge of –1.6E-19C. Note: quarks have fractional charge, but they are never observed free in nature.
  5. Be able to calculate how many electrons are or (or are missing from) an object.
  6. Know Coulomb’s law and be able to calculate the force between charges. What happens to the size of the force if the distance is 2x greater; 3x greater; 10x greater?
  7. Know that moving charge is the origin of magnetic fields.
  8. Electric fields
    1. Charge creates an electric field
    2. The direction of the field gives the direction of a forced on a + charge
    3. Force on a charge q:  F = q E   (E is made by another charge Q) [E=F/q]
  9. Electric Potential; V  (which is measured in volts = J/C)
    1. Be able to find E from V:  E = -DV/Dx
    2. Positive charge makes positive potential
  10. Circuits
    1. A battery is like a pump that raises charge up an amount V and the charge flows around the circuit.
    2. Current is the rate of flow of charge I = Q/Dt
  11. Electric materials: Know the 4 types and their characteristics

II Stars

  1. Our Sun is a hot (5700 K) ball of gas powered by fusion reactions in its core that convert hydrogen to helium
  2. Know what is meant by Luminosity. Know that the Sun’s luminosity is 3.26E26W.
  3. Know that the luminosity of a star depends on L=sAT4. How much brighter is a star that is 1.5 times hotter? How much brighter is a star that has twice the radius of our Sun?
  4. Know that hotter stars appear more blue; cooler stars are more red. The average photon energy is E=2.705 k T .
  5. Know that stars evolve.
  6. Know the following words: Photosphere, red giant, red supergiant, white dwarf, main sequence, white dwarf, Hertzsprung-Russell Diagram.
  7. Be able to locate various objects on a HR diagram
  8. Know the modern picture of temperature. More hot means more motion.

III Life in the Universe

  1. Know that there are roughly 200 billion stars in the Milky Way and roughly 200 billion other galaxies
  2. Know that the one ingredient necessary for life on Earth is liquid water. Wherever there is water, there is life (on Earth). We are included to look for life where there is liquid water (Mars, moons of Jupiter)
  3. The field of study of life elsewhere is called Astrobiology
  4. Know that the Drake equation is used to make an estimate of how many civilizations with which we might communicate

IV Quantum Mechanics Basics

  1. Electromagnetic spectrum (Radio, microwave, infrared, visible, ultraviolet, X-rays, g-rays)
    1. We see photons from 1.8 to 3.1 eV ( energy=hv; v is the frequency, h is plank’s constant)
    2. Know period, frequency, wavelength and the relation c=wavelength x frequency
  2. Inverse square law and how it explains the r2 dependence of the Coulomb force.
  3. Know that particle have a wavelength l=h/p. Be able to calculate a wavelength.
  4. All particles have a wave nature. The thing that is waving is probability.
  5. Uncertainty principle and be able to use it. Know both the DxDp and DEDt versions.

V Atoms and Nuclei

  1. Know the modern pictures for the atom and for nuclei
  2. Know that nuclei are made of protons and neutrons
    1. The number of protons determines what element
    2. The number of neutrons determines the atomic mass (N+Z)
    3. For example C-12 has 6 protons (carbon) and 6 neutrons
  3. Know that the strong force is responsible for binding nuclei
  4. The nuclear force is generated by the exchange of pairs of quarks. These pairs we call mesons. The lightest meson is the pion (dū or đu).
  5. Know that nuclei decay by the strong (alpha decay); weak (electron or positron emission); or Coulomb (fission) forces
  6. Know the half life formula for calculating how much of a sample remains after a given time
  7. If the initial fraction and half live are known, the measured fraction sometime later can be used for radioisotope dating. Be able to do a simple sample.
  8. The SI unit for radioactivity is the Becquerel (Bq = 1 decay/s)

VI The 4 forces of nature

  1. Know the four forces and their characteristics from the table on page 12 of lecture 13
  2. Be able to recognize simple Feynman Diagrams
    1. Two electrons, or protons, or other charges objects interacting via the Coulomb force
    2. A neutron decaying to a proton by the weak force
    3. Two protons (or a proton and an neutron) interacting by the strong force
  3. Be able to check reactions for Baryon conservation, lepton conservation, electric charge conservation
  4. Know what the following words means: Field theory, Quantum Electrodynamics, Quantum Chromodynamics
  5. Gravity is much weaker than the other forces and does not seem to fit in.

VII The Standard Model and Beyond

  1. Know that neutrinos interact by the Weak force, have mass, no charge, have lepton number, but don’t interact much.
  2. Antiparticles have opposite charge, baryon number, lepton number. When the meet with their like particle they annihilate giving off energy.
  3. What is the Standard Model?
  4. Review the contents of the table of particles on page 3 of lecture 15
  5. Know the three kinds of spectra and how they are made. Know that Cecilia Payne used absorption spectra to figure out what the Sun was made of.
  6. Know that string theory describes all particles are vibrations of tiny strings 10-35m in size.
  7. String theory is a possible theory of everything. It requires at least 10 dimensions to work.