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How to find the equivalent Resistance of these circuits

  1. Nov 22, 2009 #1

    Aafour

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    Suppose that all resistors have a value of 100 ohm

    how to find the equivalent Resistance of these circuits, the number in these circuits indicate the areas for which we will be completing calculations.

    how to go over these


    http://img155.imageshack.us/img155/8421/32990280.jpg [Broken]

    http://img24.imageshack.us/img24/6659/20062468.jpg [Broken]

    http://img69.imageshack.us/img69/453/10031901.jpg [Broken]

    thanks
     
    Last edited by a moderator: May 4, 2017
    Aafour, Nov 22, 2009
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  3. Nov 22, 2009 #2

    rl.bhat

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    Homework Helper

    Show your attempts.
    Do you know how to find the equivalent resistance of series and parallel combination of resistances?
     
    rl.bhat, Nov 22, 2009
  4. Nov 22, 2009 #3

    Aafour

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    rl.bhat, yes i know how to find series and parallel combination of resistances,

    for series just add the resistances, and for parallel, (1/R)=(1/R1)+(1/R2)+...

    but I really don't know how to start on these circuits listed
     
    Aafour, Nov 22, 2009
  5. Nov 23, 2009 #4

    rl.bhat

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    OK. In the case 1, two resistances are in series and this combination is in parallel with the third resistance.
    So 1/Req = 1/(R1 + R2) + 1/R3.
    In the same way try the other combination.
     
    rl.bhat, Nov 23, 2009
  6. Nov 23, 2009 #5

    Aafour

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    true, thank you. it's just that i need to draw these circuits in more easy way. thank you
     
    Aafour, Nov 23, 2009
  7. Dec 2, 2009 #6

    JakotaR

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    Hey! what about if i have the value of the equivalent resistance and want to work out the value of the 2 resistors that were previously there? cheers
     
    JakotaR, Dec 2, 2009
  8. Dec 2, 2009 #7

    rl.bhat

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    Sorry. I didn't understand your question. Give a numerical example.
     
    rl.bhat, Dec 2, 2009
  9. Dec 2, 2009 #8

    JakotaR

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    ok
    Two resistors r1 and r2 connected in parallel have an equivalent resistance of 10/3 ohms.
    When the current enters the parralell circuit it divides between the two resistors in the ratio of 2 to 1. Determine r1 and r2?
    hope u can help :)
     
    JakotaR, Dec 2, 2009
  10. Dec 2, 2009 #9

    rl.bhat

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    If 3I current flows through the parallel combination, in r1 the current is i and in r2 the the current is I2.
    The voltage across the parallel combination is V = 3I*10/3 = 10*I
    So the current in r1 = I = V/r1
    The current in r2 = 2I = V/r2
    Substitute the value of V and find r1 and r2.
     
    rl.bhat, Dec 2, 2009
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