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Few Questions on source tranformation

  1. Nov 9, 2014 #1
    It's question 1b) Please view attached

    image.jpg image.jpg

    1. Just to clarify, when different voltage sources are in series you pick the smaller one?

    2. First step, they turned the 1A and 2ohm into 2V, why does the resistance disappear? Then between the last two steps the 12/7 ohm resistance remains with 18/7 voltage. Why does one resistance disappear while the other doesn't?

    Thanks on advance
  2. jcsd
  3. Nov 9, 2014 #2
  4. Nov 18, 2014 #3


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    Staff: Mentor

    It would have been better if you'd cropped the attachment to just the relevant block in post #1 and in the process made it more legible.

    No! The 3v comes about because two sources are in series, +6v and -3v, so the resultant voltage is their sum with polarities taken into account.

    It doesn't. The solution is in error. I expect the right side 2 ohm was probably intended to be labelled 4 ohms.

    Nothing disappears. The two resistors are in parallel, so they can be replaced by an equivalent one of the value equal to that when two resistors are in parallel.

    Hope that helps.
    Last edited: Nov 18, 2014
  5. Nov 18, 2014 #4


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    Staff: Mentor

    This thread belongs in the homework sub-forum. You almost certainly would have received prompt assistance had you listed it there.

    Could a mentor kindly move this to the appropriate forum ............
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