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Why you need a integration constant

  1. Jun 17, 2012 #1
    Can someone help me with this integration?

    fysica3.jpg

    Don't understand why you need a integrationconstant.

    I would do : RTlnC = U but this isn't correct, you have to put + cte

    Why?
     
  2. jcsd
  3. Jun 17, 2012 #2
    Re: Integration

    Hallo Vdslaur
    The derivative of a Cte is 0
    When you integrate something, the result is always true up to a cte, since if you derive you will get the same answer back for any cte.
    That tells you the potential energy '0' is undefined, it's arbitrary, all that matters are its variations. in general you want to set it 0 at infinity.
     
  4. Jun 17, 2012 #3
    Re: Integration

    I know that you integrate the U but

    for exmple : the integration of dx = x + cte

    But here the integration gives you : RTlnC +cte

    So : dU = d(RTlnC)

    Solution after integration of dU = U
    Solution after integration of d(RTlnC) = RTlnC + cte

    This is right no?

    d(RTlnC) = RT d(lnC)

    And d(lnC) is the same as dx , so x + cte --> here : lnC + cte

    yes, I get it!
     
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