Review QUIZ 3

Some numbers: L ergs/second grams.

1. Conventional burning of coal releases ergs per gram of coal.

   (a) If the Sun was made completely of coal, how much energy could be extracted via the burning of the Sun?

   6 x 10**12 ergs/gram x 2 x 10**33 grams = 12 x 10**45 ergs

   (b) How long would the Sun shine at 1L if it was coal powered? Why can this hypothesis be ruled out?

   12 x 10**45 ergs / 4 x 10**33 ergs/second = 3 x 10**12 seconds -- much less than the age of the solar system.

2. What is the equilibrium in a main-sequence star?

   _xx_ Gravity balanced by thermal pressure

   ____ electrical attraction forces between the electrons and protons

   ____ Nuclear fusion balanced against gas pressure

   ____ none of the above

3. What is the energy source for the Sun's luminosity?

   ____ Mass converted into gamma rays during gravitational contraction

   ____ Helium converted into hydrogen during nuclear fusion

   ____ The decay of radioactive heavy elements like Uranium

   _xx_ Mass converted into energy during nuclear fusion reactions

4. Which of the following are true for the Sun?

   _xx_ It loses mass every second in producing the solar luminosity

   _xx_ It has a larger helium content now than it did 4.5 billion years ago when it formed

   _xx_ It is continuously ``evaporating'' charged particles into the Solar System

   _xx_ It will eventually become a Red Giant

5. In the proton-proton fusion chain, four protons get converted into one He nucleus and 2 neutrinos. During this reaction grams of matter is converted into energy. How much energy is released in this reaction?

   E = mc**2 = 0.048x10**-5 x (3x10**10)**2

   Note that the mass indicated above is released for every gram of hydrogen fused to helium.

6. When the Sun becomes a Red Giant which of the following statements will be true, which false?

   _T__ it will be more luminous than it is now

   _T__ it will have a higher He content than it has now

   _F__ it will have a higher mass than it has now

   _T__ it will have a lower surface temperature than it has now

7. What is the rate at which a star produces energy?

   2 x (2x10**33) ergs/sec

8. What is the main-sequence lifetime of a star with ?

   2/10 times the lifetime of the Sun

9. Before the core of a gas cloud can collapse into a proto-star which of the following do we think must occur?

   ____ The temperature of the cloud must be high enough to counteract gravity

   _xx_ The cloud must be shielded from the interstellar radiation field from stars (dust can provide this shield)

   _xx_ The temperature of the cloud core must reach K

   ____ The cloud core must be in hydrostatic equilibrium