Review QUIZ 3

Some numbers: L tex2html_wrap_inline116 ergs/second tex2html_wrap_inline118 grams.

  1. Conventional burning of coal releases tex2html_wrap_inline120 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 tex2html_wrap_inline122 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 tex2html_wrap_inline130 nucleus and 2 neutrinos. During this reaction tex2html_wrap_inline132 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 tex2html_wrap_inline134 star produces energy?

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

  8. What is the main-sequence lifetime of a tex2html_wrap_inline136 star with tex2html_wrap_inline138 ?

    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 tex2html_wrap_inline140 K

    ____ The cloud core must be in hydrostatic equilibrium

Michael Bolte
Sat Feb 14 22:35:57 PST 1998