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Homework Help: Electrostatics calculation help

  1. Jan 2, 2007 #1
    1. The problem statement, all variables and given/known data
    What is the radius of the orbit of an electron travelling at 9.0E6 m/s around a zinc nucleus(which contains 30 protons)?


    2. Relevant equations
    F=(kQq)/r^2
    F=QE
    ac=v^2/r
    Fnet=ma
    3. The attempt at a solution
    30 protons x 1.6E-19 = 4.8E-18 C
    electron - 1.6E-19 C

    F=ma
    F=(9.11E-31)a
    a=v^2/r
    F=[(9.11E-31)(9.0E6)^2]/r
    F=7.38E-17/r
    (7.38E-17/r)=[(9.0E9)(1.6E-19)(4.8E-18)]/r^2
    r=9.367E-11 m
     
  2. jcsd
  3. Jan 2, 2007 #2
    One more quick question:

    I know how to prove that if you move a charge twice as far away, the force will be one forth.
    [(kQq)/r^2]/[(kQq)/(2r)^2]
    (KQq4r^2)/(kQqr^2)
    =4 times as weak

    But what about if you increase the charge by twice as much, shouldn't both charges end up being 3/2 times as strong?

    [(kQq)/r^2]/[(2kQq)/r^2] I end up getting 1/2???
     
  4. Jan 3, 2007 #3
    Qucik Question, Plz Help@@@@@

    1. The problem statement, all variables and given/known data
    What is the radius of the orbit of an electron travelling at 9.0E6 m/s around a zinc nucleus(which contains 30 protons)?


    2. Relevant equations
    F=(kQq)/r^2
    F=QE
    ac=v^2/r
    Fnet=ma
    3. The attempt at a solution
    30 protons x 1.6E-19 = 4.8E-18 C
    electron - 1.6E-19 C

    F=ma
    F=(9.11E-31)a
    a=v^2/r
    F=[(9.11E-31)(9.0E6)^2]/r
    F=7.38E-17/r
    (7.38E-17/r)=[(9.0E9)(1.6E-19)(4.8E-18)]/r^2
    r=9.367E-11 m

    One more quick question:

    I know how to prove that if you move a charge twice as far away, the force will be one forth.
    [(kQq)/r^2]/[(kQq)/(2r)^2]
    (KQq4r^2)/(kQqr^2)
    =4 times as weak

    But what about if you increase the charge by twice as much, shouldn't both charges end up being 3/2 times as strong?

    [(kQq)/r^2]/[(2kQq)/r^2] I end up getting 1/2???
     
  5. Jan 4, 2007 #4

    berkeman

    User Avatar

    Staff: Mentor

    Okay, I unlocked your duplicate post and merged it here into this thread. Give me a minute to try to be helpful. Oh, and do not duplicate post again, okay?
     
    Last edited: Jan 4, 2007
  6. Jan 4, 2007 #5

    berkeman

    User Avatar

    Staff: Mentor

    Your radius calculation looks okay. Is it not matching the solution?
     
  7. Jan 10, 2007 #6
    i was just unsure on my answer and wanted to get it checked. Also, I am just unsure on how to prove algebraically how a difference in charge of one particle will effect the overall charge between the two, like I solved algebraically for the distance increase between the two.
     
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