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Electrical potential energy please help

  1. Sep 10, 2016 #1
    1. The problem statement, all variables and given/known data
    Prove that the total energy of an electron orbiting a hydrogen nucleus is Etotal = -e^2/ 8ε0 π r where e is the magnitude of charge of an electron and r is the orbital radius.


    2. Relevant equations
    Knowledge

    3. The attempt at a solution
    Here is my attempt:
    For KE,
    mv^2/r = -ke^2/r^2
    mv^2/2 = -ke^2/2r

    For PE,
    PE= k(-e)e/r - k(-e)e/∞
    =-ke^2/r
    KE+PE =-3e^2/ 8ε0 π r ,why am I wrong? please help
     
  2. jcsd
  3. Sep 10, 2016 #2

    haruspex

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    Is the left hand side there positive or negative? What about the right hand side?
     
  4. Sep 10, 2016 #3
    LHS is positive and RHS is negative? They should both be positive as the negative sign represents the direction?I don't get it
     
  5. Sep 10, 2016 #4

    haruspex

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    So the right hand side must be wrong. Try explaining in detail how you arrive at the minus sign there.
     
  6. Sep 10, 2016 #5
    Thanks for helping me. But why the minus sign in potential energy need not to consider?
     
  7. Sep 10, 2016 #6

    haruspex

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    That is not an energy expression, it's a force expression.
     
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