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Series and parallel components

  1. Jul 21, 2017 #1
    Hi guys, how do I figure out whether components are in series/parallel with each other just by looking at them? for example, in the circuit on the picture I posted, how do I know which of the resistors are in series/ parallel with eachother? I know the definition involves nodes, but in clear, accurate sentences, when are components in series/parallel with each other?
    Thank you :).
     

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  3. Jul 21, 2017 #2
    A series connection is one where the current has no other path other than to the next component. Parallel is when both the positive and negative sides of each component are connected to each other.
     
  4. Jul 21, 2017 #3
    Thanks for ur reply :).
    So a component is in series w/ another component when the current flowing from one of the components does not flow through a junction to reach the other? and can you elaborate on the parallel components part?
     
  5. Jul 21, 2017 #4

    davenn

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    no, the opposite

    almost
    keep it simple, forget about the positive and negative .... referring to the OP's cct .... resistors are not polarised

    @xJJx

    your circuit has a mix of series and parallel

    upload_2017-7-22_10-45-32.png

    we will guide you here at PF, but we would like you to make a good effort to work this out yourself :smile:

    so for a start identify some series resistors and then identify some that are in parallel

    hint ... some of the series resistors can be added together to make a simpler circuit


    Dave
     
  6. Jul 22, 2017 #5

    sophiecentaur

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    @OP The words "series " and "parallel" are not actually necessary in discussing big circuits. It is a handy way to deal with what goes on in a small part of a circuit. You have probably got a text book of web page with examples of series and parallel pairs of resistors and you are having a problem with zooming out and looking at the circuit as a whole. Never try to think "R1 and R2 and in series and in parallel with R3 and R4 and they are all in parallel with R5 and R 6, which are in series . . . . . . . ." You will fall over if you try it that way.
    Look up Series and Parallel equivalent circuits. This link is one of many. Read it through and don't scan. Follow the video through and don't get distracted as you go through. There is light at the end of the tunnel. :smile:
     
  7. Jul 26, 2017 #6
    Thanks for all your replies! I'm learning series/parallel circuits atm so I have to look at the circuit that way. I've guessed that the top two resistors are in series w/ each other, the bottom two are in series and them 4 resistors are in parallel with the 2 ohms resistor, but that's just a lucky guess. I also know how to combine resistors. My problem is finding specific definitions/rules for what makes components in series/parallel with each other. Can anyone give me this?
     
  8. Jul 26, 2017 #7

    Averagesupernova

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    The 2 ohm resistor is in series with the network of 4 resistors. Not parallel like you say.
    -
    Imagine sliding the resistors physically together on the schematic until they run into each other and become one resistor. That would be in series. Their combined resistance adds. Do that with both the upper and lower resistors and then go from there. Redraw the circuit several times if necessary.
     
  9. Jul 27, 2017 #8

    sophiecentaur

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    Post #2 gives perfectly reasonable rules for working it out.
    If you can draw a dotted line around a pair of resistors, to include their connections, it is easy to apply those rules to decide whether they are series or parallel connected. Alternatively, rather than asking for some sort of bomb-proof rule, just look at some of the thousands of examples that Google will throw up and use the 'machine learning' method of finding a rule that works. Learning this sort of thing 'by numbers' is really not the best way, you know. You need to be after some understanding and not just learning rules.
     
  10. Jul 27, 2017 #9

    jim hardy

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    In my day we worked countless homework problems to drill it into our heads.
    The mechanics of doing it make it intuitive.
    One usually needs to reduce a circuit like yours to its simplest equivalent , perhaps to find the load on a battery. Or perhaps just to accustom himself to reading circuit diagrams. We old guys forget when it was all so new to us.

    Here's the step by step process you should go through for your circuit, actually redrawing it for every step.

    series_parallel.jpg

    That's how you learn to think like an electron oops make that 'think like a charge carrier' .

    Then some wise guy will hand you this

    series_parallel2.jpg

    and ask you
    "Are that battery and that resistor in series or are they in parallel ?"
    Which deserves the reply :
    "Mr Wise Guy, I'll answer that question with a question. Who said the terms series and parallel are mutually exclusive?
    Kindly rephrase your question using conjunction AND not OR . Then my one word reply will be 'Yes' . "

    Those two thoughts from post 2 work very well. Ask them as questions and trace out the current path.
    I've used them since 1961.

    old jim
     
    Last edited: Jul 28, 2017
  11. Jul 28, 2017 #10

    sophiecentaur

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    OH yes!!!
    The problem these days is that students are not exposed to endless homework questions. Reason? Questions have to be marked and teachers have less and less 'free' time on their timetables to do that (more class time and time spent doing lesson plans to prove they are working hard enough - plus lots of other reporting tasks). Consequently, students are not in the habit of actually doing problems. It's very convenient to plug the numbers into a simulation and to get the answer without really knowing how you got it.
    So we can't blame young people for their attitude. They acquire it as a result of the way they're taught.
     
  12. Aug 18, 2017 #11
    Thank-you all so much for your replies! they were very helpful. Yeah I agree there's no 'concrete rules' out there for this, I kind of just guessed and got it right most of the time.
     
  13. Aug 18, 2017 #12

    jim hardy

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    thanks for the feedback !
     
  14. Aug 18, 2017 #13
    you were very helpful! :)
     
  15. Aug 18, 2017 #14
    Hi, I agree. I've done many examples before which I got right most of the time, but I was curious to find out if there actually are any rules on how to determine series/parallel components. My lecturer stated some rules one time but then contradicted himself in the next lecture which confused me. So after doing some examples, I tried to find some rules which I wrote:

    How you can determine if components are in series or parallel with each other, without having any of their current, voltage, resistance etc values:

    Components are in series with each other if they have the same current flowing through them (i.e. if there are NO junctions between these components, since the current splits at a junction, causing there to be less/different current flowing through the other component). Components in series with each other must also share at least one node with each other.

    Components are in parallel with each other if they don’t have the same current flowing through them (I.e. if there is at least one junction between these components, since the current splits at a junction, causing there to be less/different current flowing through the other component). Components in parallel with each other must also share only two nodes with each other.


    N.B: When I say ‘junction’, I do NOT mean ‘node’, I mean a point where the current can split.

    N.B: The current in a circuit flows from the point of highest voltage to the point of lowest voltage.




    Can anyone tell me if there's anything wrong here ^?
     
  16. Aug 18, 2017 #15

    jim hardy

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    You have the tune , lyrics could stand a little polish .

    That requires there be no path or junction or node where a current split could happen.

    That forces them to experience the same voltage. "Directly" might be a long crooked wire or serpentine line on a schematic ; just make sure it's continuous.

    Think in small baby steps one thought per sentence.
    This basic concept is one where the plumbing analogy will help you . Soon it'll be intuitive so you can move on past the water analogy and its pitfalls..
     
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