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Hard intro circuit problem! help please! im stuck on this one for hrs!

  1. Feb 28, 2013 #1
    http://imageshack.us/photo/my-images/585/circuitzzz.png/

    i thought maybe i should ignore everything that is on the right side of the 3v and just focus on the left side. but this one is not looking too good for me.

    any ideas on this one??
     
  2. jcsd
  3. Mar 1, 2013 #2

    Simon Bridge

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    Re: Hard intro circuit problem! help please! im stuck on this one for

    It looks like it should respond to mesh analysis.
    What's the problem?

    One way to sort your head out about this sort of problem is to redraw the circuit in a way that makes more sense to you. Since there is an explicit ground in this diagram, it may help to draw a ground rail across the bottom of the page and draw the other components in above that ... i.e. the ground rail has three resistors connected to it...
     
  4. Mar 1, 2013 #3
    Re: Hard intro circuit problem! help please! im stuck on this one for

    find volt across the 2mA source
     
  5. Mar 1, 2013 #4
    Re: Hard intro circuit problem! help please! im stuck on this one for

    how many mesh loops do we have here??
     
  6. Mar 1, 2013 #5

    ehild

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    Re: Hard intro circuit problem! help please! im stuck on this one for

    Yes, it is a good idea. See picture.

    ehild
     

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  7. Mar 1, 2013 #6

    Simon Bridge

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    Re: Hard intro circuit problem! help please! im stuck on this one for

    A fair few - but you don't need all of them.
     
  8. Mar 1, 2013 #7
    Re: Hard intro circuit problem! help please! im stuck on this one for

    I1 = V/R
    Resistors add up right?
    I1 = 3/3+3+2+3+2
     
  9. Mar 1, 2013 #8
    Re: Hard intro circuit problem! help please! im stuck on this one for

    i found i1 = 0.6409 A
    i2 = 0.2307
    total Resistance = 13.588Ω

    so i1 - i2 x total R = volt across the 2mA?

    is that correct
     
  10. Mar 1, 2013 #9

    ehild

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    Re: Hard intro circuit problem! help please! im stuck on this one for

    No.
    Only resistors in series add up. There is I2 current flowing through the left 2kΩ resistor. It is not in series with the other ones.

    ehild
     
  11. Mar 1, 2013 #10
    Re: Hard intro circuit problem! help please! im stuck on this one for

    i see, so what do i do? im not sure how to solve I1, i think i did I2 correctly though
     
  12. Mar 1, 2013 #11
    Re: Hard intro circuit problem! help please! im stuck on this one for

    i think i got it, since one of the nodes are grounded out

    I1 = 3/6+5 = 0.2727A right?
     
  13. Mar 1, 2013 #12

    ehild

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    Re: Hard intro circuit problem! help please! im stuck on this one for

    Write KVL for the loop in the figure, and substitute I2 = I1+2

    ehild
     

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  14. Mar 1, 2013 #13
    Re: Hard intro circuit problem! help please! im stuck on this one for

    applying KVL = 6I1 - 3 +5I1 + 2I2= 0?
     
    Last edited: Mar 1, 2013
  15. Mar 1, 2013 #14

    ehild

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    Re: Hard intro circuit problem! help please! im stuck on this one for

    yes.


    ehild
     
  16. Mar 1, 2013 #15
    Re: Hard intro circuit problem! help please! im stuck on this one for

    it should be .002 right? because 2 mA = .002 A. after i got the currents, what would the total resistor be to plug in the equation V = i x R?
     
  17. Mar 1, 2013 #16
    Re: Hard intro circuit problem! help please! im stuck on this one for

    Also I got I1 = -0.2727A and I2 = 1.727A
    do i add them together to get the the current i need to solve the problem?

    1.727 + (-.2727)?
     
  18. Mar 1, 2013 #17

    ehild

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    Re: Hard intro circuit problem! help please! im stuck on this one for

    You substituted the resistance in kΩ-s, then the currents must be in mA.

    What should be 0.002?

    ehild
     
  19. Mar 1, 2013 #18
    Re: Hard intro circuit problem! help please! im stuck on this one for


    oh i see. i thought it was KVL = 6I1 - 3 +5I1 + .002I2= 0
     
  20. Mar 1, 2013 #19
    Re: Hard intro circuit problem! help please! im stuck on this one for

    im not sure what im suppose to do after i got the currents though
     
  21. Mar 1, 2013 #20

    ehild

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    Re: Hard intro circuit problem! help please! im stuck on this one for

    You multiply the current with the resistance to get voltage.
    Have you got the currents? What are they?

    ehild
     
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