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Homework Help: Electron Near Nucleus

  1. Sep 18, 2008 #1
    I am sure it is easy to do, but I just can't seem to figure the question out. It is 4 parts and I got the first 2 parts. If someone can give me the steps with the numbers (already handed in assignment, and got it incorrect), that would be much appreciated.

    1. What is the magnitude of the electric field at a distance of 3.10 ×10-10 m from a neptunium nucleus?
    The answer I got is 1.39×1012 N/C.

    2. What is the magnitude of the force on an electron at that distance?
    2.23×10-7 N F=qE.

    3. Treating the electron classically, that is, as a point object that can move around the nucleus at reasonably slow speeds, what is the period of the electron's motion?
    The answer is 2.23×10-16 s but I am unable to calculate this.

    I tried taking the Force from part 2 and using F=ma. Then using a to find velocity. Then used that to find T.

    4. Again treating the electron classically, how fast it it moving?
    The answer is 8.72×106 m/s, again no idea what I did wrong but I can't find this answer.

    Many thanks.
  2. jcsd
  3. Sep 18, 2008 #2
    I wouldn't start with F=ma for question 3. I think F = mv2/r would do the trick.

    Once you have v you can work out what the distance is for the electron to make one complete orbit (hint, you already have the radius).

    And then of course, speed = distance/time.

    This gives the answers to both (3) and (4)
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