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Find the current I in this electrical circuit

  1. Dec 6, 2017 #1
    1. The problem statement, all variables and given/known data
    2yjwtqt.jpg
    2. Relevant equations
    V = I.R

    3. The attempt at a solution
    6 ohm and 3 ohm are series = b
    Then b pararel to 9ohm = c = total resistance
    b = 9ohm
    c = 9/2 ohm
    I = V/R
    I = 9.6/c
    I = 2,13 A

    Can you help me?
    Is it right? My friend's answer is 0,8
     
  2. jcsd
  3. Dec 6, 2017 #2

    BvU

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    If you leave out the 3 and 6 the current is already more than 1 A, so your friend must be wrong :smile:
     
  4. Dec 6, 2017 #3
    How about the exact answer?
     
  5. Dec 6, 2017 #4

    BvU

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    I'm not a betting man, nor a teacher. You have to convince yourself !
     
  6. Dec 6, 2017 #5

    BvU

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    Le me ask: what do you get when you leave out the 6 and the 9 ? :rolleyes:
     
  7. Dec 6, 2017 #6
    I = V/R
    I = 9.6/9 = 1.06 ??
     
  8. Dec 6, 2017 #7

    BvU

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    What about the wire from the top to the 3 ohm ? Wouldn't the current prefer to through that instead of through the 6 ohm ?
    ( leaving out the 6 and 9 leaves only the 3 ! )
     
  9. Dec 6, 2017 #8

    cnh1995

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    They are not.

    Can you see anything special about the 6 ohm resistor?
     
  10. Dec 6, 2017 #9
    Wouldn't the current go to both branches? Im still really not good at it. But why only 3?
    I = 9.6/3 = 3.2 A?
     
  11. Dec 6, 2017 #10
    Yes, i think so. Maybe because the current from 1st branch go to 6ohm, and the current from 2nd branch go to 6 ohm too? So they're not series...?
    If pararel then I = 9.6 / (18/11) = 5.8 A?
     
  12. Dec 6, 2017 #11
    What normally works for me is to re-draw the circuit (e.g. in the drawing I attached). Maybe now you can see what cnh1995 meant with "special" on the 6Ω-resistance?
     

    Attached Files:

  13. Dec 6, 2017 #12

    BvU

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    The word is parallel.
    Hwat is 11/18 ?
    How far are you now ? Can you see the 6 ohm is short-circuited ? There is a wire from one end to the other. That wire makes the potential at both ends equal -- no current through the resistor. You can leave it out of the diagram without anything changeing. Then things look simple again ...
     
  14. Dec 6, 2017 #13
    Oh parallel.. thanks
    3ohm and 9ohm are parallel, the total resistance is 9/4
    I = 9.6 / (9/4)
    I = 4.2 A is it?
     
  15. Dec 6, 2017 #14

    BvU

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    As in #4: you have to convince yourself !
    (But I like this one a lot :wink: !)
     
  16. Dec 6, 2017 #15
    Ok.. we can conclude it as 4.2 A. Thank you
     
  17. Dec 9, 2017 #16
    To be honest, i think i still get wrong. My answer is not among the options..
     
  18. Dec 9, 2017 #17

    gneill

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    What options are available?
     
  19. Dec 9, 2017 #18

    cnh1995

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    You have chopped off some decimal places.
    What are the options?
     
  20. Dec 9, 2017 #19

    epenguin

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    Is an option 5⅓ A?
     
  21. Dec 9, 2017 #20
    What is the potential difference across the six ohm resistor. Under what circumstances can you remove the six ohm resistor from the circuit
     
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