Astronomy 122&, Fall 2009

Homework C: Due Monday, September 21.

Part I: Multiple choice. On your scantron fill out your NAME, STUDENT NUMBER, and NETWORK ID both in writing and in the bubbles. In addition, fill out "FORM C."

1. Which particle carries the negative electric charge?
a) only the electron
b) only the neutron
c) only the proton
d) both the proton and the neutron
e) both the proton and the electron

2. Which particles have nearly the same mass?
a) electron and proton
b) proton and neutron
c) neutron and electron
d) none of the above three
e) all the above three

3. Which force holds protons and neutrons together in an atomic nucleus?
a) gravity
b) strong
c) weak
d) electromagnetic
e) all the above

4. Which force holds the electron to the nucleus?
a) gravity
b) strong
c) weak
d) electromagnetic
e) all the above

5. The kind of chemical element is determined by the number of
a) protons in the nucleus
b) neutrons in the nucleus
c) neutrons + protons in the nucleus
d) neutrons + electrons in the nucleus
e) protons + neutrons + electrons in the nucleus

6. The second lightest of all elements is
a) iron
b) helium
c) carbon
d) hydrogen
e) lithium

7. Isotopes of the same chemical element have different numbers of
a) neutrons
b) electrons
c) protons
d) muons
e) fractons

8. The isotope of uranium U-238 has 238
a) protons
b) neutrons
c) electrons
d) protons plus neutrons
e) protons plus electrons

9. An ion is an atom with missing or extra
a) protons
b) neutrons
c) electrons
d) all of the above
e) none of the above

10. A nucleus of the carbon isotope carbon-14 has 6 protons. How many neutrons does it have?
a) none b) 2 c) 6 d) 8 e) 48

11. The last (heaviest) stable chemical element is
a) uranium
b) oxygen
c) lead
d) bismuth
e) radium

12. Which is the correct order from shortest-wave (highest- energy) radiation to longest-wave (lowest-energy) radiation.
a) radio, X-ray, gamma-ray, blue light, red light
b) gamma-ray, X-ray, blue light, red light, radio
c) radio, blue light, red light, gamma-ray, X-ray
d) radio, infrared light, blue light, X-ray, gamma ray
e) infrared light, radio, blue light, red light, gamma- ray

13. Which color light refracts the least?
a) blue
b) violet
c) red
d) yellow
e) ultraviolet

14. A blackbody
a) reflects all radiation that falls upon it
b) refracts all radiation that falls upon it
c) absorbs all radiation that falls upon it
d) just sits there doing nothing
e) is invisible to the eye

15. If you double the temperature of a heated solid body, it will radiate how many times more energy?
a) 2 b) 4 c) 8 d) 16 e) 32

16. Of those listed below, a body at 5 degrees Kelvin can produce only
a) radio radiation
b) visible light
c) ultraviolet
d) X-rays
e) gamma rays

17. Absorption and emission lines are caused by energy changes in atomic and molecular
a) electrons
b) neutrons
c) protons
d) both protons and neutrons
e) both electrons and neutrons

18. The H-Beta Balmer line is formed by a transition between levels
a) 1 and 2
b) 2 and 3
c) 1 and 3
d) 2 and 4
e) 2 and 5

19. The age of the Sun, Earth, and Solar System are calculated to be
a) 40,000 years
b) 45 million years
c) 550 million years
d) 4.5 billion years
e) 45 billion years

20. We know the ages of the meteorites (asteroids that hit the Earth), hence the age of the Earth and the Solar System, from
a) ancient writings found in the Pyramids but long kept hidden by a government conspiracy
b) the decays of radioactive elements
c) where on Earth they are found
d) their speeds of entry into the Earth's atmosphere
e) how long it now takes them to go around the Sun

Part II. Show all your work.

1. At what wavelengths (in appropriate units) will the following blackbodies have their radiation maxima? (See p. 126.) What then is the dominant kind of radiation (radio, X-rays, etc.) Give the first example in units of centimeters, the others in Angstroms.
a) T = 10 K (about the temperature of a dense interstellar molecular cloud);
b) T = 2000 K (the temperature of the coolest normal star);
c) T = 5780 K (the temperature of the solar surface);
d) T = 50,000 K (about the temperature of the hottest normal star);
e) T = 1,000,000 K (the temperature of a neutron star).

2. The Sun's surface temperature is 5780 K. What is the total energy flux (energy radiated per unit area per second) from the surface of Regulus (T = 12,000 K) relative to that of the Sun?

3. Use your diffraction gratings to examine a variety of light sources and describe and draw the results. In particular, look at incandescent, mercury vapor, and sodium vapor street lights and compare them. Also try as variety of "neon" signs.

4. a) A hundred-inch telescope gathers how many more times light than does a 20-inch telescope?
b) Why do single-dish radio telescopes have poorer resolving power than optical telescopes?