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Homework Help: Electronics (Diodes + capacitors) questions

  1. Mar 20, 2008 #1
    I've been working through our physics book for year 12 Physics, and only just now when we've hit electronics has it really confused me. I'd like to be able to understand it before our current 2 week school break ends.
    Perhaps the biggest flaw of the book is that it doesn't say how it got answers, it only says what the answer is.
    So if I can get help with this, I might post a few more I'm having trouble with. Hopefully I'll be getting the hang of it very soon. When the teacher explains it to me in class I can get it, but it seems every question I hit has some new element that the book has never explained.

    1. The problem statement, all variables and given/known data
    http://img209.imageshack.us/img209/9649/q11fg1.jpg [Broken]
    http://img209.imageshack.us/img209/308/q12pj6.jpg [Broken]

    2. Relevant equations

    3. The attempt at a solution
    I looked at the answer in the book, it's something very similar to this:
    http://img206.imageshack.us/img206/2451/q1atp0.jpg [Broken]
    I tried to find the numbers they got, but the only thing I could thing of was C=Q/V, and I don't have a C or a Q to put in there.
    And the graph confused me.
    I'm not sure how they got the numbers they got, why the graph does what it does, or what that little U symbol means.
    Could someone please explain how and why for me? Thank you very much.
    Last edited by a moderator: May 3, 2017
  2. jcsd
  3. Mar 20, 2008 #2
    [tex]C = \frac{Q}{V}[/tex]
    [tex]I = C\frac{dV}{dt}[/tex]
    I = slope * C
    Last edited by a moderator: May 3, 2017
  4. Mar 20, 2008 #3


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    The current and voltage in a capacitor are related by a differential equation: [itex]i(t)=C\frac{dv(t)}{dt}[/itex]. Try to find this section in your book and study it.

    The [itex]\mu[/itex] sign is a prefix meaning "one-millionth."
  5. Mar 20, 2008 #4
    So if I use either of those formulas...
    I = C*(dV/dt)
    I = 10*(5/1)
    I = 50
    I get 50, mA I presume. But how did they get -100 as well, and the graph they've got?
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