Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

Resistors in series, parallel or?

  1. Sep 14, 2015 #1
    Hello Forum,

    When resistors are introduced, it is explained that they can be either in series or in parallel configuration. In series means that the are traversed by the same current and one of the terminals of each resistor is connected to the other's terminal( I am saying that because there can be two resistors in a circuit that are traversed by the same current but not be in series).

    In parallel means that the terminals of two resistors are connected to each other and to a wire/conductor that is equipotential while the other two terminals are also interconnected to a wire that equipotential as well but at a different potential than the other wire. The voltage drop across both resistors is the same.

    I believe that two or more resistors can be connected in such a way that they are not in series neither in parallel, i.e. they don't have the same voltage drop and are not traversed by the same current....Is that correct? I think so...
    Do you have any good example?

    Thanks,
    fog37
     
  2. jcsd
  3. Sep 14, 2015 #2

    anorlunda

    User Avatar
    Science Advisor
    Gold Member

    Maybe you draw a picture of thst arrangement for us.
     
  4. Sep 14, 2015 #3
    Ok, see the attachment. The top resistor is neither in series or in parallel with any of the two lower resistors (which are in series)....

    This should confirm my initial thinking...
     

    Attached Files:

  5. Sep 14, 2015 #4

    Averagesupernova

    User Avatar
    Science Advisor
    Gold Member

    There has been a thread on similar subjects here on PF. If a single battery and a single resistor are hooked together, are they in series or are they in parallel? Definitions are very important when we start nit-picking about these things. Like anorlunda said, let's have a pic. :)
    -
    Edit: Ooops, you beat me to it.
     
  6. Sep 14, 2015 #5

    anorlunda

    User Avatar
    Science Advisor
    Gold Member

    Nice try, but no cigar. The bottom two resistors are in series. Replace them with a single resistance equal to the sum of the two. Call it the bottom resistor. Now the top resistor is in parallel with the bottom resistor.

    We can repeat this combine and replace transformation many times in complex arrangements.
     
  7. Sep 14, 2015 #6

    Averagesupernova

    User Avatar
    Science Advisor
    Gold Member

    It also depends on where we attach the rest of the circuit. A wise person once told me that 'everything is relative'.
     
  8. Sep 14, 2015 #7
    Ok, I see your point anorlunda.

    But to the question "is the top resistor in series or in parallel with the first lower resistor" the answer is neither since they are not run by the same current or share the same voltage drop. I guess I am considering pairwise comparisons. MY point is that it is possible to connect one element (be it a resistor or something else) into a circuit so that it can be in series, in parallel with another specific element or neither. It is not a binary choice between being in series and being in parallel...
     
  9. Sep 14, 2015 #8

    anorlunda

    User Avatar
    Science Advisor
    Gold Member

    I see what you are trying to say. But you won't win arguments or score points on exams saying it that way.
     
  10. Sep 14, 2015 #9
    More interesting, if you want, is solving complicated networks of resistors like the infinite ladder, etc... I wasn't familiar with those complicated cases until today.

    See http://www.phy6.org/Electric/-E6-Resistors-2.htm where it says "Not all resistor circuits can be resolved into combinations of resistors in parallel and in series. Consider a "classical" problem appearing in many textbooks: A 10V voltage is appliedbetween opposite corners (A,B) of a cubeconsisting of 12 resistors of 1Ω each. How much current will flow--or in other words, what is the equivalent resistance R between A and B?......This circuit cannot be resolved into separate resistors in parallel and in series (at least not in the usual way)....."
     
  11. Sep 14, 2015 #10

    meBigGuy

    User Avatar
    Gold Member

    You are correct in saying that grouping all resistor connectivity topologies into series or parallel is not complete if you are considering networks of resistors. In that case, the networks are in series or parallel. And, even that gets shaky when you consider bridge circuits.
     
Know someone interested in this topic? Share this thread via Reddit, Google+, Twitter, or Facebook




Similar Discussions: Resistors in series, parallel or?
  1. Series or Parallel? (Replies: 2)

Loading...