Help needed with Total Resistance

Discussion in 'Homework Help' started by avonbath, Sep 17, 2011.

  1. avonbath

    Thread Starter New Member

    Sep 17, 2011
    3
    0
    Hi,

    I am new to electrical circuits. I have a few class assignments that I need to do which involve the calculation of total effective resistance. I have attached the drawings below, would appreciate some help and please kindly explain your answers.

    Many thanks.

    LS :)
     
  2. mik3

    Senior Member

    Feb 4, 2008
    4,846
    63
    The first and the second are a piece of cake! The third needs a bit more effort!

    Have a go and show us your work.
     
  3. praondevou

    AAC Fanatic!

    Jul 9, 2011
    2,936
    488
    As Mik said the first two don't even need to be calculated.

    The third you should redraw to become more obvious how the resistors are connected. If you have a closer look all resistors have one connection to the left and one to the right, so they are all in .... parallel.
     
  4. mik3

    Senior Member

    Feb 4, 2008
    4,846
    63
    You sould not reveal the answer. Let him think first!
     
  5. avonbath

    Thread Starter New Member

    Sep 17, 2011
    3
    0
    Thanks Mik and Praondevou,

    I am a 11-yr old who just starting learning electricity in school and am pretty confused with the topic. I would be really grateful if you could enlighten me.

    Qns (1) & (2):
    I have problem identifying a short circuit. I am unsure if circuit (1) & (2) are one. If they are, does it mean that total resistance for (1) & (2) = zero?

    Qns (3):
    I did try redrawing the circuit but no matter how hard I tried, I just couldn't come up with something that makes more sense. And the fact that it comprises of two similar circuits which look just like Qns (1), I am beginning to wonder if (3) would even work or it is just another more sophisticated short circuit.

    Please help, I would be very grateful.

    Many thanks.
     
  6. justtrying

    Active Member

    Mar 9, 2011
    329
    353
    I find it helpfull to "think like a current" when looking for a short circuit - start tracing current flow on your diagram with arrows, this will help to determine where the nodes are and where the resistors split into parallel arrangements. A short will happen when there is a wire with no resistance - current will preferrentially flow through it as it is the easiest path. But be ware! Always redraw the diagram given to you as the nodes may not be obvious and may lead you to wrong conclusions (hint: q3 looks like all resistors are shorted out, as you mentioned). With practice you will figure out a method that works for you.
     
  7. avonbath

    Thread Starter New Member

    Sep 17, 2011
    3
    0
    Thank you, Justtrying. I will write down what I think are the answers to the questions and hopefully, the teacher could shed some light if I am wrong.

    Thank you. Appreciate it.
     
  8. Jony130

    AAC Fanatic!

    Feb 17, 2009
    3,962
    1,097
    In Q3 all resistor are connect in parallel
     
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