1. Not finding help here? Sign up for a free 30min tutor trial with Chegg Tutors
    Dismiss Notice
Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

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

    Astronuc

    User Avatar

    Staff: Mentor

    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

    Astronuc

    User Avatar

    Staff: Mentor

    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
    hmm
    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

    Astronuc

    User Avatar

    Staff: Mentor

    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.

    http://hyperphysics.phy-astr.gsu.edu/hbase/nuclear/elescat.html

    http://hyperphysics.phy-astr.gsu.edu/hbase/nuclear/scatele.html

    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
Know someone interested in this topic? Share this thread via Reddit, Google+, Twitter, or Facebook

Have something to add?