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Homework Help: What does In equal?

  1. May 28, 2008 #1
    What does "In" equal?

    In a RL circuir time constant formula what does the "In" indicate? This is probably very simple but it has got me stumped. Such as t=TIn(E/Vl). All help is appreciated!
  2. jcsd
  3. May 28, 2008 #2


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    Staff: Mentor

    Thread moved to Homework Help forums.

    Welcome to the PF, Bryan. I'm not sure what your equation represents. As described at this web page:


    the time constant for an LR circuit is L/R. Could you please review that web page, and then if you still have a question, please post more information about the equation you are asking about.
  4. May 28, 2008 #3

    The Electrician

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    Gold Member

    ln stands for "natural logarithm". It looks like you have a letter "I" rather than lower case "L" in In. It should be ln, or Ln, or LN.

    On my calculator, LOG stands for base 10 logarithms and LN stands for natural logarithms.

    So your formula might be rewritten to avoid confusion as t=T*LN(E/Vl)
  5. May 28, 2008 #4
    RL circuit formula?

    Could someone explain to me this formula?




    I get 20/14.57=1.372683596
    where and how do you get 2.38, where does the 1n fall in and how? is there a numerical value for this statement? Please help?
  6. May 28, 2008 #5
    the electrician already explained. its called natural log. In your calculator natural log.
    Its not 'In', the symbol is Ln, or some people write L as 'l', and unfortunately 'l' looks like 'I'

  7. May 28, 2008 #6
    hopefully you already understand this bryanehli, if not... a little further help...

    Ln relates to 'e' and hopefully you recognize that. if not... look in a book.

    e^(Ln(x)) = x
    Ln(e) = 1
  8. May 29, 2008 #7
    Another interesting thing about e, aka Euler's Number, is this:

    f(x) = e^x
    f ' (x) = e^x
  9. Jun 13, 2008 #8
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