Voltage Divider worksheet #18

Discussion in 'Homework Help' started by sbixby, May 29, 2010.

  1. sbixby

    Thread Starter Active Member

    May 8, 2010
    57
    10
    First post for me... I'm reading Tony's DC volume and going along in the worksheets. I feel sheepish asking this, but I'm confused about the results of "Question 18" in the HTML version of the current Voltage Dividers worksheet. (http://www.allaboutcircuits.com/worksheets/e_divide.html)

    To whit, the circuit diagram is: [​IMG]

    The symbology, to me, implies that we measure the voltage from V.out to a common ground, but when I look at that, the voltage from (lower-left-most) ground to V.out is going to be zero.

    Yet, the answer says -12.5v. Therefore, I believe I'm misunderstanding this circuit. Searching for the symbology of the triangles used as ground in this circuit shows "signal ground", which I don't really understand.

    What am I missing here?
     
  2. Ghar

    Active Member

    Mar 8, 2010
    655
    72
    What makes you say that the voltage is going to be zero?
    A voltage of zero means the two points (ground and Vout) are at the same potential.

    This generally happens because there is no current flowing through the resistors which isn't the case here.
     
  3. sbixby

    Thread Starter Active Member

    May 8, 2010
    57
    10
    Oh, that was dumb. I was literally picturing a wire from V.out 'dot' to ground, rather than voltage from that (unconnected) dot to ground.

    Thanks for the spiderweb clearing question for a question. :)
     
  4. R!f@@

    AAC Fanatic!

    Apr 2, 2009
    8,754
    760
    heee hee hee

    Op is using positive ground...he is confusing himself
     
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