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Homework Help: Electron scattering find acceleration

  1. Oct 9, 2006 #1
    Lead nucleus has charge = +82e
    and raadius R = 7.10*10^(-15) m
    permittivity of free space = 8.85*10^(-12) C^2/Nm^2
    magnitude of charge on electron e = 1.60*10^(-19) C
    mass of electron = 9.11*10^(-31) kg

    find the acceleration 4R from the center of the lead nucleus.

    how do i do this?

    F = kqQ/(r^2) then a = F/m doesnt work out. im not sure if im using the correct values for the q and Q though.
  2. jcsd
  3. Oct 9, 2006 #2


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    a = F/m should work.

    What values are you using for Q (nucleus) and q (electron)?

    For electron q = e = -1.60*10^(-19) C

    For the nucleus, it depends if one is considering the shielding of the electrons or not. Q on the nucleus = Ze = +82e = 82*1.60*10^(-19) C.

    At 4R, where R is the effective radius of the nucleus, the electron probably experiences the full coulombic field of the nucleus.

    And in the denominator, r2 would be (4R)2
  4. Oct 9, 2006 #3
    thank you.

    i got to this point, but now i am confused about how it would be different if it were R/4 instead of 4R.

    the equation is different i think, but i cant figure out what it would be.
  5. Oct 9, 2006 #4


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    If r = 4R, then r2 = 16R2, and 1/r2 = 1/(16R2)

    If r = R/4, then r2 = R2/16, and 1/r2 = 16/R2.
  6. Oct 9, 2006 #5
    i entered that in before though, and it said my answer was incorrect.

    isnt there a difference for when r>=R and r<R?
  7. Oct 9, 2006 #6


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    Well, yes. When r < R, then the electron is within the nucleus and it would be interacting with a completely different and more complex charge field than outside the nucleus.



    Have you solved the classical EM problem for an electric field in a sphere of uniformly distributed charge and compared to the E-field outside? The nucleus is more complex.
    Last edited: Oct 9, 2006
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