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Using electric force to calculate number of protons

  1. Mar 6, 2008 #1
    [SOLVED] using electric force to calculate number of protons

    1. The problem statement, all variables and given/known data
    a hydrogen nucleus and a nucleus of an unknown atom are stationary, 5.0x10^-10m apart, the electric charge on the hydrogen nucleus is 1.6x10^-19C.
    express the charge you have calculated for the unknown nucleus as a whole number multiple of the charge on the hydrogen nucleus, you may assume this number is the atomic number of the unknown nucleus, ie the number of protons




    2. Relevant equations
    I used Fe= -ke Q1 Q2 / r^2




    3. The attempt at a solution

    my calculation gave me the charge on the unknown nucleus to be -2.39x10^-19C
    however, when i try to turn this into some whole number compared to 1.6x10^-19, i either get 1.5 or 0.6, neither of which are whole numbers.
    please help with this part of the question, even if its just a nudge as to what on earth is actually being asked.....
    neither integers nor any similar work appears in my coursebook and my tutor isnt returning my emails.
    please help
    1. The problem statement, all variables and given/known data



    2. Relevant equations



    3. The attempt at a solution
     
  2. jcsd
  3. Mar 7, 2008 #2

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    How? Data seems to be missing here.
     
  4. Mar 7, 2008 #3
    full equation

    okay, so using Fe = -Ke Q1 Q2 / r^2

    Fe = 5.5x10^-9 N
    -Ke = -9.0x10^9 Nm^2C^-2
    Q1 = 1.6x10^-19C
    r^2 = 6.25x10^-20m^2

    Q2 = 5.5x10^-9 x 6.25x10^-20 / -9.0x10^9 x 1.6x10^-19

    Q2 = -2.39x10^-19C

    but the main part of the problem is the part where i have to use the 2 number for Q to tell how many protons Q2 nucleus has... i just arent sure where to start with that part
     
  5. Mar 7, 2008 #4

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    This was not previously mentioned.

    How, with the given value of r=5.0x10^-10m?
     
  6. Mar 7, 2008 #5
    ah-haa!

    that was it, that was what was causing all my problems. i thought that because it said they were 5.0x10^-10m apart i thought that was the diameter, and that i wanted the square of the radius.... i just calculated it all again and i get it now.... its carbon...

    thanks muchly

    big hugs in cyberspace
     
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