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REMINDERS

REMINDERS . Exam II next Thursday, April 14! Practice exam posted on website - Same format as first exam – Multiple Choice & Short Answer Review session (Q & A only) Tuesday, April 12 @ 7 pm Location: normal lecture hall in Physics. REMINDERS .

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REMINDERS

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  1. REMINDERS • Exam II next Thursday, April 14! • Practice exam posted on website - Same format as first exam – Multiple Choice & Short Answer • Review session (Q & A only) Tuesday, April 12 @ 7 pm Location: normal lecture hall in Physics

  2. REMINDERS • Exam II next Thursday, April 14! • Practice exam posted on website - Same format as first exam – Multiple Choice & Short Answer • Review session (Q & A only) Tuesday, April 12 @ 7 pm Location: normal lecture hall in Physics

  3. REMINDERS • Exam II next Thursday, April 14! • Practice exam posted on website - Same format as first exam – Multiple Choice & Short Answer • Review session (Q & A only) Tuesday, April 12 @ 7 pm Location: normal lecture hall in Physics

  4. Discussion REVIEW plan • 1 Chapters covered • 2 Main equations to know • 3 Brief overview & summary • 4 Sample discussion questions • 5 Sample multiple choice

  5. Material Covered • Chapter 5 – Light, interaction with matter, telescopes • Chapter 10 – The Sun • Chapter 11 – Stars – overview / properties • Chapter 12 – Stellar evolution • Chapter 13 – Deaths of stars • Textbook, lecture notes, discussion section activities!

  6. Important Relations L ~ M 3 E = hc / λ = h * frequency photon T ~ 1 / λ peak distance = 1 / parallax 4 2 2 4 L = 4 π r σ T ~ r T 2 Brightness or Flux ~ 1 / (distance)

  7. Key things to Memorize: • Equations already mentioned • EM spectrum • HR diagram (most time on main sequence) • Life cycle of a low & high mass stars • Stellar Cutoffs – 8 M, 2 M, 1.4 M, 3 M • Types of spectra & how they are formed • Structure of our SUN • What makes the sun shine? Evidence for nuclear fusion in the core. • H fusion – (4 H → 1 He + energy + neutrinos) • Spectral Sequence, luminosity class - OBAFGKM

  8. Key Concepts: • Longer wavelength photon → lower E • Shorter wavelength photon → higher E • Hydrostatic Equilibrium • Radiation pressure, degeneracy pressure (electron and neutron) vs. gravity • Doppler Effect • Distance determination – distance modulus, parallax

  9. Key Concepts (continued): • Bohr atomic model – explaining absorption/emission through electron transitions • Telescopes improve with collecting area and angular resolution • Positive nuclei repel, so high T required in stellar cores for fusion of heavier and heavier elements • Solar thermostat • Main sequence is a sequence of MASS

  10. Essay topics may include: • Describe the evolution of a low mass/high mass star • Draw and label an HR diagram • Emission/Absorption/Continuous spectra – Describe how each is produced • Newton’s form of Kepler’s 3rd law – calculating stellar masses • Binary star systems

  11. Essay topics may include: • Inverse square law (Flux vs. Luminosity) • Doppler shift • Describe Heliocentric Parallax and discuss the limits of this method • Why do we put telescopes into space? • Why does the sun shine? • What is the sun’s structure?

  12. Other stuff to emphasize:

  13. Know GENERAL idea ONLY:

  14. Concept Overview & Summary

  15. Identify the following portions of the Electromagnetic spectrum: The electromagnetic spectrum Figure 3.5 B A C D E

  16. Which end of the spectrum is more energetic, A or B? Why? The electromagnetic spectrum Figure 3.5 B A

  17. Gamma rays X-rays Ultraviolet Visible Infrared Microwaves Radio SHORT Wavelength ( λ ) HI Frequency ( ν or f ) LONG Wavelength ( λ ) LOW Frequency ( ν or f )

  18. These two pictures describe what? “photon” & wave

  19. Light has aDUAL NATURE! “photon” & wave Energy of photon = (Planck’s constant) x (frequency) or (c / λ)

  20. If the Hydrogen gas cloud is moving towards Earth, the absorption line marked will shift in which direction? An absorption line of Hydrogen measured at rest A B

  21. How do light and matter interact? KNOW THESE DEFINITIONS! • Emission • Absorption • Transmission • Reflection or Scattering

  22. What does this diagram illustrate? Electromagnetic radiation Figure 3.8

  23. What types of light spectra can we observe? • Continuous spectra • Absorption spectra • Emission spectra

  24. Which is the absorption spectra?

  25. Which is the continuous spectra?

  26. Which is the emission spectra?

  27. Which spectrum is coming from the coolest object? BLUE Yellow RED BLACK

  28. At what wavelength does the peak of the yellow spectrum lie? What type of star might this be? BLUE Yellow RED BLACK

  29. Is the star producing the yellow or red spectrum hotter? Why? BLUE Yellow RED BLACK

  30. Which spectrum is coming from the hottest object? BLUE Yellow RED BLACK

  31. Which star is more luminous? T = 15,000 K Radius = 1 unit T = 15,000 K Radius = 2 units

  32. Which star is more luminous? T = 15,000 K Radius = 1 unit T = 3,000 K Radius = 1 unit

  33. Which star is more luminous? T = 12,000 K Radius = 1 unit T = 3,000 K Radius = 7 units

  34. REMEMBER! Luminosity of a star is intrinsic. Depends on Temperature & Radius. L ~ R T 4 2

  35. For which stars would we observe a Doppler Shift? A B C

  36. Doppler shift Figure 3.18

  37. Doppler Effect Summary Motion toward or away from an observer causes a shift in the observed wavelength of light: • blueshift (shorter wavelength)  motion _______ you • redshift (longer wavelength)  motion AWAY from you • greater shift  greater speed

  38. Doppler Effect Summary Motion toward or away from an observer causes a shift in the observed wavelength of light: • blueshift (shorter wavelength)  motion toward you • redshift (longer wavelength)  motion ______ from you • greater shift  greater speed

  39. How do telescopes help us learn about the universe? • Telescopes collect more light than our eyes  light-collecting area • Telescopes can see more detail than our eyes  angular resolution • Telescopes/instruments can detect light that is invisible to our eyes (e.g., infrared, ultraviolet)

  40. Angular Resolution • The minimum angular separation that the telescope can distinguish.

  41. What is this diagram illustrating?

  42. Why can parallax only be used for nearby stars?

  43. Are the emission lines locatedin the UV part of the spectrum or the IR part of the spectrum?

  44. Which is the correct explanation for the sun’s shining? Is it on FIRE? Is it powered by NUCLEAR ENERGY? Is it CONTRACTING?

  45. E = mc? - Einstein, 1905 In Einstein’s famous equation, what should the exponent be? This means that a ‘lil bit of mass can be converted to a LOT of energy

  46. The balance of the inward force of gravity with the outward force of pressure due to radiation is referred to as ?

  47. Solar wind A) Corona B) Chromosphere C) Photosphere D) Core Give the approximate Temperatures of each Of these layers.

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