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Homework Help: Voltages of a,b, and c

  1. Aug 10, 2016 #1
    1. The problem statement, all variables and given/known data
    See image attached

    I dont understand why Va is 20 volts instead of it being 5 volts or a combination of the two. The same goes with Vb. I can see (but I am likely looking at it the wrong way) why Vc is 8 volts.. Because Vc is right next to the voltage source.

    Can anybody please explain how I get to these correct answers? Thank you.

    2. Relevant equations

    3. The attempt at a solution
    See 1

    Attached Files:

  2. jcsd
  3. Aug 10, 2016 #2


    User Avatar

    Staff: Mentor

    Hi Josh225. The voltages are referenced to the earthed point; it is assigned to be 0V and everything else is referenced to that.

    In the absence of instructions to the contrary, we always assume the earth to be the zero volts node. So when we say another node is at X volts it is understood that this is w.r.t. the circuit's earth.

    Vab = Va - Vb = 5V
    Va = Va - Vearth = 20V - 0V = 20V
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