Review Questions for Exam 2

These questions are intended to make you think about the relevant topics for the exam. They are not necessarily the exam questions themselves.

The exam will consist of about 30 multiple choice questions and around 5 short answer questions. The questions will primarly address topics covered in the lectures and the lecture notes should be your primary guide to preparing for the test. The readings in Bennett should help clarify the lecture notes. The test will contain a few general questions from the readings from the web. This test covers material in lectures 11 through 19 as outlined on the lecture notes web page. Note: All relevant equations will be provided at the top of the exam.

You may want to review the important mathematics page for examples of some of the quantitative questions that may appear on this test -- particularly concerning light and thermal radiation.

The relevant sections in the Cosmic Perspective textbook are: Chapter 3 (all sections); Chapter 4 (read section 4.3 lightly); Chapter 5 (section 5.3 lightly); Chapter 6 (section 6.1 lightly)

Web readings:

What did the Greeks know about the nature of the Earth and Solar System? What were the major contributions of Copernicus, Tycho Brahe, Galileo, Kepler, and Newton? What is the Scientific Method? Can you cite an example?

What are Kepler's Laws of planetary motion? How do you draw an ellipse? What is meant by the eccentricity of an ellipse? At what special point in a planet's elliptical orbit do you locate the Sun? How does a planet's speed vary depending on where it is in its elliptical orbit? What equation relates a planet's orbital period to its distance from the sun?

What are Newton's three laws of motion? What does Newton's first law say should happen to a ball being swung in a circle on a string if the string should break? How are mass, force, and acceleration related? How would you define mass given Newton's second law? (Ans: an object's resistance to being accelerated by a force)? What does Newton's third law have to do with rocketry?

How does the gravitational force depend on the separation between a pair of objects? on the mass of each object? Why did Newton postulate that a force must act on the Moon to keep it in its orbit? (Ans: because it does not travel in a straight line at constant velocity -- i.e. the first law)

How is an orbit related to continuous falling? Why do astronauts appear weightless? Why do objects of different mass fall at the same rate? What does swinging a ball in a circle on a string have in common with a spacecraft orbiting the Earth? (Ans: they are effectively the same thing. In the case of the ball the string is exerting a force equivalent to that provided by gravity in an orbit).

How does the orbital velocity depend quantitatively on the distance a planet is from the Sun? How can gravity and orbits be used to measure the mass of the Sun? How about the mass of a planet? If you were left in intergalactic space with a one kilogram mass, in principle, could you measure your mass?

How long does it take a satellite in low earth orbit to complete an orbit around the Earth? How fast is it going? Why must you be out of the Earth's atmosphere in order to orbit the Earth? How high is that (that is, how high above the Earth's surface does a satellite orbit). What is a geostationary satellite? Why is it so easy to see satellites in the morning or evening sky?

How does the Moon raise tides on the Earth? Why on both the side toward the Moon and the side away from the Moon? Why are there two high tides a day? Why is the day getting longer due to tidal effects? Why does the Moon turn on its axis at a rate which is exactly matched to its orbital motion around the Earth? How long is a "day" on the Moon? Why will total solar eclipses no longer occur at some point in the moderately distant future?

What are the primary regions of the Electromagnetic spectrum (ordered by either increasing or decreasing wavelength)? How do you define wavelength and frequency? How is the energy of a photon related to its wavelength? How are the wavelength and frequency of a photon related to each other? Which photons are more energetic? Red or blue? Radio or ultraviolet?

How does the peak wavelength (i.e. color) of the light emitted by a hot solid object (thermal radiation) depend on its temperature? If a source of thermal radiation is at room temperature (300K) in what part of the electromagnetic spectrum does it emit most of its light? How does the brightness of the light emitted by a hot solid object depend on its temperature? How much brighter does a source of thermal radiation get if you triple its temperature? What does the temperature of an object actually measure?

Why do atoms produce spectral lines of very specific colors? Why is this set of colors unique to each element in the periodic table? If an electron moves from a higher energy level to a lower one does the atom emit or absorb a photon? What kind of spectrum do you see if you look at a hot glowing blackbody through a tenuous cloud of gas? Why do we see dark spectral lines in the spectrum of the Sun?

What is the Doppler shift? What does it permit you to measure? Does a Doppler shift occur if the object is moving across your line-of-sight (neither toward you or away from you)? Will an object moving in a perfect circle around you produce a Doppler shift? What's the difference between a "redshift" and a "blueshift"?

What is the primary purpose of a telescope? Ans: to collect light. How does the light collecting ability of a telescope depend on its diameter? What's the difference between a refracting and a reflecting telescope? Can you sketch either type? Why are all of the large telescopes in use today of the reflecting variety?

How does the resolution of a telescope depend on its size? Can you explain why radio telescopes need to be so large (think about the wavelength of radio light compared with visible light)? Why is the Hubble Space Telescope so much more effective than a telescope on the ground even though the Hubble telescope is only 1/4 the size of the biggest telescopes on the ground? Why must some forms of astronomy (Infrared, Gamma Ray, X-ray, for example) be conducted from space?