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Please Help, Physics

  1. May 13, 2011 #1
    1. Suppose that Cepheids did not exist and there were no other standard candle technique that worked at the same distances. Which statement would be true?

    a. We would not be able to measure the distances of distant galaxies.
    b. We would still be able to measure the distances of distant galaxies using Hubble's law, but we would not be able to use white dwarf supernovae.
    c. We would still be able to measure the distances of distant galaxies using white dwarf supernovae, but we would not be able to use Hubble's law.
    d. We would still be able to measure the distances of distant galaxies, but not of nearby galaxies.
    I think it is a or d.

    2. Why do we use Hubble's law to estimate the distances of most distant galaxies, rather than using white dwarf supernovae in all cases?

    a. We have not observed white dwarf supernovae in most galaxies.
    b. We can detect white dwarf supernovae only in relatively nearby galaxies.
    c. Hubble's law gives a more reliable estimate of distance than white dwarf supernovae.
    d. We could use either method for any galaxy, but Hubble's law is simpler.
    I think b or c.

    3. Imagine that radar had never been invented and that we instead had to rely on a less reliable method of measuring distances in our solar system. If that method led us to underestimate the Earth-Sun distance by 10%, how would it affect other measurements in the distance chain?

    a. Parallax would also be off by 10%, but the other methods would be just as accurate.
    b. The error in radar would affect our measurements in the solar system, but it would have no effect on measurements with the other techniques.
    c. Parallax would then be off by 20%, main-sequence fitting by 30%, Cepheids by 40%, and so on.
    d. They would all be off by the same 10%.
    I think c or d.

    4. Which technique is the most useful for measuring the distance to a galaxy located 10 million light-years away?

    a. parallax
    b. Cepheids
    c. main-sequence fitting
    d. white dwarf supernovae
    I think it is b.
  2. jcsd
  3. May 14, 2011 #2


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    Homework Helper

    lbtocth, I think you need to give us more of your thinking than just which choice you think is right. It looks too much like you are just asking others to do your homework for you. Say what you know about Cepheids and how the distance is measured. Have a go at assessing the limitations in range for the method. Maybe doing that will give you a definite answer!
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