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Homework Help: Inductance Question

  1. Mar 5, 2007 #1
    1. i = 10te^(-5t), at what instant of time is the current maximum?

    first I differentiated i, using the product rule.

    di/dt = (10e^(-5t)) (1-5) , thats what I got after simplifying, im pretty certain this is correct. My confusion comes in when taking natural logarithms.

    if ln(e(^1)) = 1 then ln(e(^-5t)) = -5t, im just not entirely sure what to do from here but I gave it a shot.

    10ln 5t(1-5) = 0

    ln (50t-250t) = 0**

    ln (50/250) = t.

    The answer in the book is di/dt = 0 when t=1/5.

    If anyone can clear any of that up for me Id be very grateful.

    I have just spotted a glaring error** the 10 should be taken as a power, not a product.

    so it should be ln((5t/25t)^10) = 0

    how do I calculate t?
    Last edited: Mar 5, 2007
  2. jcsd
  3. Mar 6, 2007 #2


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    Your differentiation di/dt = (10e^(-5t)) (1-5) is wrong.

    It should be di/dt = (10e^(-5t)) (1-5t)

    Fixing that mistake makes the question a lot easier!
  4. Mar 6, 2007 #3
    ahhhh thankyou, I really should double check more often. I was nearly pulling my hair out over that!
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