physics - parallel electric circuits

Discussion in 'Homework Help' started by 999kola, Apr 25, 2011.

  1. 999kola

    Thread Starter New Member

    Apr 25, 2011
    2
    0
    Problem:
    Three resistors, values 35, 45, and 85 ohms, are connected in parallel across a 35 V battery. What is the current through the 35 ohm resistor?

    Attempt:
    R total = 35+45+85 = 165
    I total = 35V/165ohms = .2
    I for 35 ohms = 35V/35 ohms = 1


    I'm not sure if this is right or not, but it doesn't seem right to me. I understand how to get the total current, but I'm no sure how to get it for only 1 resistor in a parallel circuit.
     
  2. bertus

    Administrator

    Apr 5, 2008
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  3. Adjuster

    Well-Known Member

    Dec 26, 2010
    2,147
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    Well, clearly the total current can't be less than what's flowing in one resistor, so what's wrong?

    The current through the 35Ω resistor is correct. Unless you are told that the battery has internal resistance, the presence of the other resistors makes no difference to the current in the 35Ω.

    You are wrong about the total resistance though. This is a parallel circuit. Req = 1/(1/R1 + 1/R2 + 1/R3)
     
  4. 999kola

    Thread Starter New Member

    Apr 25, 2011
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    Oh, now I feel silly! Thanks so much, that answered my question.
     
  5. designnut

    Member

    Apr 21, 2011
    33
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    for parallel circuits you add currents, not rersistances.
    1 + .777 +.259 = 2.037
    r= 1/ (1/35 + 1/45 +1/165





















































































































    add currents not resistances. Rp= 1/ (1/35 + 1/45 +1/165) - 17.588
     
  6. wmodavis

    Well-Known Member

    Oct 23, 2010
    737
    150
    As stated by others your answer to the question was correct but your other 'non-answer-to-the-question superfluous information' was incorrect. Some good analysis by others. The good thing about your 'other' information is it shows some of the mis-conceptions you have need some fixing. And that is the beauty of this forum. Help comes by asking.
     
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