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Voltage between two points

  1. Nov 27, 2015 #1
    1. The problem statement, all variables and given/known data

    What is the voltage between P and Q?

    2. Relevant equations

    3. The attempt at a solution

    Don't know how to begin. I thought maybe I could walk around the circuit to se how the potential changes. Is that a good idea?
  2. jcsd
  3. Nov 27, 2015 #2
    You should know Ohms law and how to add resistors in parallel and series configuration.
  4. Nov 27, 2015 #3
    yes I know how to do that. How should a solve this problem?
  5. Nov 27, 2015 #4
    Hi Drizzy:

    I think the way the figure is drawn makes it tricky to see what resistances are in series and in parallel. I suggest a layout that shows one resistor with the 12 volts across it, and
    the other three resistors as a series of two parts: one with one resistor, and the other with two resistors in parallel.

    Good luck.

  6. Nov 27, 2015 #5
  7. Nov 27, 2015 #6
    As you can see resistor 15_ohms and 20ohms share the same nodes, so they are parallel thus can replaced by equivalent resistor.
  8. Nov 27, 2015 #7
  9. Nov 27, 2015 #8
  10. Nov 27, 2015 #9
    I know that the voltage across the to parallell resistors is 12 aswell. So the current going through it is 12/68,57..

    then I can multiply it with 60/7

    Is that right?
  11. Nov 27, 2015 #10


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    No, there is also a voltage drop across the 60 Ω resistor.
  12. Dec 1, 2015 #11
    Hi Drizzy:

    The diagram linked in your post #7 show two resistances in series. You want to get the voltage drop across one of them. You don't need to calculate any currents. The same current goes through both resistors. You already know the sum of the voltage drops across both resistors.

    Hope that helps.

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