profc.jpg (13600 bytes)Use these questions to test your understanding. If you get them wrong, you will be linked back to the relevant part of the notes. 
Be sure you study them thoroughly (don't just get a quick fix for your mistake) so your overall understanding is improved.





1. Suppose you go outside and look at three stars. Star A is blue, star B is white, and star C is red. Which star is the hottest and which is the coldest?

a. A is hottest and B is coldest       b. C is hottest and A is coldest    c. B is hottest and C is coldest     d. A is hottest and C is coldest

2. If a star is moving away from you at constant speed, how do the wavelengths of the absorption lines change as the star gets farther and farther?

a. they get farther and farther to the red      b. they move toward the blue      c. they stay shifted the same amount to the red

3. If the emission lines in one object are more strongly blueshifted than those from a second object, then the first object is moving

a. into hotter regions      b. toward us faster then the second object is     c. we cannot tell how it is moving just from its emission lines

d. toward us slower than the second object is

4. An object which emits light with a peak wavelength at 500nm has a temperature _____ that of an object whose emission peaks at 250nm. ( 1nm = 10-9 meters)

        a. the same as        b. 4 times         c. 2 times          d. one half         e. Cannot be computed from the information given.

5. Two stars are identical in all respects but one: Star A is three times further away from us than Star B. What are the relative brightnesses of these two stars?

        a. Star A is three times fainter than Star B

        b. Star B is three times fainter than Star A

        c. Star A is nine times fainter than Star B

        d. Star B is nine times fainter than Star A

        e. The stars appear equally bright

6. A box contains a collection of molecules (for example, the box might be full of air). We have a gauge that records how much force is exerted on the walls of the box by molecules. We take data for awhile and then notice that the force increased. What happened?

a. nobody knows

b. the temperature decreased

c. the pressure decreased

d. the temperature increased

e. some molecules escaped from the box

7. If you know the wavelength of a photon, you can compute

a. its position       b. its frequency      c. its energy       d. its position, frequency, and energy      e. its frequency and energy

8. At what temperature does an object produce radiation?

a. 212 F or 100 C         b. 32 F or 0 C           c. 5500 K         d. at no temperature      e. at any temperature above absolute zero

9. Which of the following moves the fastest?

a. blue photons       b. red photons        c. x-rays         d. radio waves        e. all of the above move at the same speed

10. Visible light comprises

a. nearly the entire electromagnetic spectrum

b. only a small portion of the electromagnetic spectrum

c. the lowest energy portion of the electromagnetic spectrum

d. the highest energy portion of the electromagnetic spectrum

e. none of the electromagnetic spectrum

11. The number of visible emission lines with different wavelengths that an atom can produce

a. is always one       b. is always two      c. is always three       d. is always four

e. depends on the numbers and arrangements of electrons in the atom

12. Electrons have a wave character which means that

a. they can only exist in selected orbits within atoms

b. they are not particles

c. they cannot have an electrical charge

d. they must be found only outside atoms

e. they have the same mass as protons

13. Hydrogen absorption lines in the spectrum of the source indicate that


        a. there is a cloud of hydrogen behind the source

        b. there is a cloud of hydrogen in front of the source

        c. the source is exciting nearby hydrogen

        d. the source is made of hydrogen

        e. the source is shining on a cloud of hydrogen off to one side


14. When we say photons and electrons have "wave-particle duality", it means


        a. some of them act like waves, some act like particles

        b. photons and electrons are coupled, with the electrons acting like waves and the photons as particles

        c. any photon and any electron can act like a wave or a particle depending on the circumstances

        d. they are all particles but they move up and down like waves

        e. a photon and an electron can interfere with each other


15. The "luminosity" of a source is


        a. how bright it appears to be

        b. its total energy output

        c. its average temperature times its area

        d. the energy it emits in the visible spectral range

        e. the energy of the photons at the peak of its output