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KE of electron being attracted by 2 protons

  1. Jun 13, 2006 #1
    Hi everyone,

    I have a problem regarding this question. An electron is and it is being attracted to 2 stationary protons. The 2 protons are at a vertical distance of 6x apart and the electron passes through the centre of the line joining the 2 protons (3x below the top proton and 3x above the bottom proton), and at right angle to that line. The electron is released at a distance of 4x from the vertical mid-point of the 2 protons. What is the max KE of the electron?

    I found the potential at the mid point of the 2 protons which the electron will pass through to be at e/6(pi)(Enot)x, and eV is the KE so it gives e^2/6(pi)(Enot)x. The answer is wrong and the one I've been given is a 15 at the denominator and not 6. Can anyone point out my mistake? thanks!
     
    Last edited: Jun 13, 2006
  2. jcsd
  3. Jun 13, 2006 #2

    nrqed

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    It's because you forgot to take into account the fact that the electron has some potential energy at the initial position!
    At the initial position, it is at a disatnce of 5x from both proton. Find the potential energy there. Then use conservation of energy and you will see that you will get ther answer (hint: 1/6 -1/10 = 1/15).

    Patrick
     
  4. Jun 13, 2006 #3

    nrqed

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    It's because you forgot to take into account the fact that the electron has some potential energy at the initial position!
    At the initial position, it is at a disatnce of 5x from both proton. Find the potential energy there. Then use conservation of energy and you will see that you will get ther answer (hint: 1/6 -1/10 = 1/15).

    Patrick
     
  5. Jun 13, 2006 #4
    Thanks Pat for the help I can't imagine I didn't thought of that and to think that my final exams are in november! Thanks agaiN!
     
  6. Jun 13, 2006 #5

    nrqed

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    You are very welcome!
     
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