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Calculate the equivalent resistance in the Figure

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  1. Mar 27, 2017 #1
    1. The problem statement, all variables and given/known data
    upload_2017-3-27_9-10-48.png

    2. Relevant equations / 3. The attempt at a solution
    Here is my attempt from the homework assignment. It doesn't appear that I got any points for this question and was hoping to get a little help in correcting my issues or pointed in the right direction to start over.

    upload_2017-3-27_9-16-8.png
     
  2. jcsd
  3. Mar 27, 2017 #2

    cnh1995

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    Can you spot the resistors in parallel? Parallel resistors will have their ends connected between the same two points.

    The red diagram is the correct one. Is that the provided answer?
     
  4. Mar 27, 2017 #3
    I'm not sure what the correct answer is. I'm also confused in my TA's diagram why it has 4 resistors?
    There only 2 resistors that are in parallel, right?
     
  5. Mar 27, 2017 #4

    cnh1995

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    No.
    There is one more. Look carefully.
     
  6. Mar 27, 2017 #5
    OK, thinking out loud here:
    It looks like he was simplifying the circuit?
    I can see that we should be able to combine resistors to make an easier diagram (which is how we go from 5 Resistors to 4 Resistors in the red). I'm a little confused on the orientation and how we have 3 Resis. in parallel.

    I doodled it out but I can't see how it is simplified to make 3 resis. in parallel instead of the 2 obvious resistors.
    Why isn't R5 in series with the R2 and R3,4 combination now?
    upload_2017-3-27_9-54-4.png
     
  7. Mar 27, 2017 #6

    cnh1995

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    How is R3 connected to R4? Check their ends.
     
  8. Mar 27, 2017 #7
    They're connected in series, so can't you add them together and make it equivalent to a resistor with a sum of their resistances?
    eg. R3,4=R3 + R4
    and then this new resistor is in series with R1?
     
  9. Mar 27, 2017 #8

    cnh1995

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    No. Check their ends. Aren't they connected between the "same" two points?
     
  10. Mar 27, 2017 #9
    Is it because of the diagonal line, does that indicate that the first end point of R3 is the same end as the first end point of R4?
     
  11. Mar 27, 2017 #10

    cnh1995

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    Exactly!
     
  12. Mar 27, 2017 #11
    Sweet!!
    OK, so now I have the diagram looking like the figure below, but where does the R5 fit in? It's in series with R2, R3, and R4 also, right?
    So, is it R1 and R5 that can be combined in series like I said before?
    upload_2017-3-27_10-49-48.png
     
  13. Mar 27, 2017 #12

    cnh1995

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    R2 is not in parallel with R3 and R4. In fact, you'll see something interesting about R2.

    Which three are in parallel?
     
  14. Mar 27, 2017 #13
    R1 is in series with R2 which is in series with R5, right?
     
  15. Mar 27, 2017 #14

    cnh1995

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    No.

    Which three are in parallel?

    What does the diagonal wire do to R2?
     
  16. Mar 27, 2017 #15
    The diagonal would cause a short circuit so there would be no resistance through R2
    because the current would go through the path of least resistance, the diagonal wire
     
  17. Mar 27, 2017 #16

    cnh1995

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    Right.
    Which three are in parallel?

    I believe you'll be able to find the equivalent resistance now.
     
  18. Mar 27, 2017 #17
    Oh gosh, Then R1, R3, and R4 are the parallel resistors
    Then, 1/Rtot=1/R1 + 1/R3 + 1/R4
     
  19. Mar 27, 2017 #18

    cnh1995

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    No.
    (And that leaves only one combination:biggrin:.)

    Check the ends of the resistors. If they are connected between the same two points, they are in parallel.
     
  20. Mar 27, 2017 #19
    Oooh so would the points work out equivalently like this?
    upload_2017-3-27_11-46-45.png
     
  21. Mar 27, 2017 #20

    cnh1995

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