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Circuits - DC Power pack (6-pin) questions?

  1. Sep 10, 2015 #1
    1. The problem statement, all variables and given/known data
    mcummq.jpg

    2. Relevant equations
    While equations should be unnecessary to solve these questions, I am not sure if I have done so properly.

    3. The attempt at a solution
    Well, I placed my answers on the paper already. I am unsure about the potential difference between 12V and 5V, as since neither are grounded, I'm not sure how they have any frame of reference to compare to one another. I'm also not sure about the next 2 questions since only the 5V pin is grounded, but I feel based on my familiarity with circuitry, so long as the 5V and 12V were attached to each other, my answers are correct. Any advice on the right way to look at these (or if I am looking at them wrong and got any wrong answers) would be greatly appreciated.
     
  2. jcsd
  3. Sep 10, 2015 #2

    donpacino

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    Gold Member

    smart questions...
    look at it this way. If there are 12V between +12 and com, and there are 5V between +5 and com, then there will be 7 v (like you said) between +12 and +5. in order for a voltage to be "12V" it has to be "12V" above something else. Voltage is a relative measurement.

    all your answers look correct!
     
  4. Sep 10, 2015 #3
    Well thank you for the feedback. I just wanted to make sure I was looking at it correctly, as the whole concept of a ground being necessary in a circuit as a reference point and some of this not having that reference point threw me a bit off.
     
  5. Sep 10, 2015 #4

    NascentOxygen

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    Staff: Mentor

    How did you determine (d), the potential between -12v and COM?
     
  6. Sep 10, 2015 #5
    I think I messed up and thought the question was asking the same thing as (c), but with the -12V instead of 12V. After you made me take another look at it, I'm now thinking it should be -12V for (d).
     
  7. Sep 10, 2015 #6

    NascentOxygen

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    How would you explain what circuit arrangement or connections lie behind the pin labelled GROUND?
     
  8. Sep 11, 2015 #7

    donpacino

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    oops, I didn't catch that either :/
     
  9. Sep 12, 2015 #8

    NascentOxygen

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    Staff: Mentor

    Yes, it is -12V.
     
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