impedence calculation

Discussion in 'Homework Help' started by kdswalia, Dec 10, 2015.

  1. kdswalia

    Thread Starter New Member

    Dec 8, 2015
    2
    0
    1.what is the impedance of an ac circuit that has a voltage of 120v, and an inductive reactance of 300 ohms and a capacitive reactance of 500 ohms?
    (700ohms,400ohms,200ohms,800ohms)
    2.Determine the impedance of a circuit that has a resistance of 300 ohms and capacitive reactance of 500ohms?(800ohms,5831ohms,3400ohms,0ohms)
    3.A circuit has a reactance of 300 ohms and an inductive reactance of 383 ohms. what will the impedance of the circuit be?
    (48.65ohms,486.5ohms,4865.1ohms,683ohms)
    help me calculate this in the simplest form high school level.
     
  2. WBahn

    Moderator

    Mar 31, 2012
    17,751
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    This is not Homework Done For You. So you need to show YOUR best attempt to at least start to figure these out. It doesn't have to be complete or correct, but it provides a basis for us to see how you are approaching the problem and where you are going right and wrong so that we can try to steer you onto a path that will lead you where you are trying to go.
     
  3. kdswalia

    Thread Starter New Member

    Dec 8, 2015
    2
    0
    I have absolute no idea how to do this
     
  4. WBahn

    Moderator

    Mar 31, 2012
    17,751
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    So you've never heard of impedance or reactance and have never seen anything regarding how to work with them?

    If so, then why are you even trying to answer questions like these? That would be like me trying to answer questions from a test about nuclear propulsion system design, having never had anything to do with the topic. There would be no point in it or in asking other people to show me the answers. I would simply lack too much of the foundational knowledge for it to be of any use whatsoever.
     
  5. Bill B

    Active Member

    Nov 29, 2009
    61
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    Can you do simple subtraction and solve right triangles?
     
  6. Cyrenaica —

    New Member

    Jun 7, 2015
    16
    2
    hi !

    i suggest you to devote approximately 3 hours of your life to read these great http://www.allaboutcircuits.com/textbook/alternating-current/ articles ( chapters 2 , 3 and 4 ) , on how to understand what is going on and how to absolutely correctly handle these simple test - questions

    and first question in tests is not fully explained - how do these elements are connected in the circuit ? and the value of voltage is not needed at all . and about third question , it is not fully explained too . so circuit contains " reactance " ( ? ? ? ? what kind reactance ) and an " inductive reactance " . . .

    wish you luck ! !
     
  7. WBahn

    Moderator

    Mar 31, 2012
    17,751
    4,799
    Sadly, the questions almost certainly reflect the poor mathematical rigor common whenever a course works with impedance and reactance this way. Treating inductive and capacitive reactance both as positive quantities distinguished only by what name is given to them is a recipe for disaster, but people working at this level (including many instructors teaching at this level) fail to appreciate this because the tools they use only let them work one level at a time and so they have gotten used to being limited to only working one level at a time.

    The third question almost certainly has a typo (probably a transcription error as the TS typed it in) and it specifying a resistance of 300 Ω.

    Also, the list of answers for the second problem appears to have one (possibly two) typos in it, namely a missing decimal point.

    The connection details of the circuit in Question #1 is a non-issue. Think of it as a black box and that block box has a certain impedance and that impedance is composed of a resistance and a reactance. Regardless of how the components are actually organized, the definition of impedance places the resistance and the reactance conceptually in series.
     
    Cyrenaica — and Bill B like this.
  8. Bill B

    Active Member

    Nov 29, 2009
    61
    0
    He did mention this was high school level. Its very basic at any rate. No mention of phase angles which you'll need for solving circuits with any complexity. WBahn is right. Without understanding the concept, doing the math is essentially useless.
     
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