Our Evolving Universe
Self Test 4

1. Nuclear fusion generates energy because
   1. it produces neutrinos
   2. one helium nucleus weighs less than four hydrogen nuclei
   3. one helium nucleus takes up less space than four hydrogen nuclei
   4. helium is heavier than hydrogen
   
   
2. Hydrogen fusion is more efficient than helium fusion because
   1. hydrogen is much more abundant
   2. helium is an inert gas
   3. helium fusion needs higher temperatures
   4. the fractional mass difference is larger
   
   
3. More massive stars are more luminous because
   1. they have more hydrogen available
   2. they have higher central temperatures so the reaction rate is higher
   3. they fuse heavier elements as well as hydrogen
   4. more than one of the above
   
   
4. When the Sun has used up all the hydrogen in its central core,
   1. it will start fusing hydrogen just outside the central core
   2. it will start fusing the helium that has accumulated in the core
   3. it will explode
   4. it will collapse into a white dwarf
   
   
5. Because helium fusion is less efficient than hydrogen fusion
   1. helium fusing stars are less luminous
   2. the helium fusion stage doesn't last very long
   3. helium fusing stars have lower surface temperatures
   4. more than one of the above

out of 5.

Go back to Summary of Lecture 4
Go on to Summary of Lecture 5
Go back to main page