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

Homework Help: Reducing Circuits to Their Simplest Form

  1. Apr 11, 2010 #1
    1. The problem statement, all variables and given/known data
    Which of the following circuits could be reduced to a single resistance and a battery by determining the equivalent resistance using combinations of resistors in series and parallel?
    Screenshot.png

    A. II and IV only
    B. I and II only
    C. II and III only
    D. I and III only
    E. I and IV only


    2. Relevant equations

    Parallel: 1/Req = 1/R1+1/R2+...
    Series: Req= R1+R2+....

    3. The attempt at a solution

    I think 3 and 4 can be eliminated because it seems impossible that you can reduce those to just one resistor.

    So I'm thinking the answer is I and II only, but I'm unsure.
     
  2. jcsd
  3. Apr 11, 2010 #2
    Take a closer look at 4. Redraw it (hint: it'll have 3 parallel resistor branches).
    For 2, are you planning to use the delta to Y transformation?
     
  4. Apr 11, 2010 #3
    I dont even know what you mean by the delta to Y transformation :redface:
     
  5. Apr 11, 2010 #4
    Don't worry about it then :) It's a transformation that would allow you to change circuit 2 into battery+resistor circuit. Since you said you thought it could be solved, how did you plan on reducing on?
     
  6. Apr 11, 2010 #5
    well the resistors on the outer edges of the diamond are in series. You can reduce those to one resistor each. Then you have 3 resistors in parallel which you can reduce...i think
     
  7. Apr 11, 2010 #6
    For circuit 2? That wouldn't be correct. Every resistor is connected to nodes (point where 3 or more wires meet) at both of its ends. You can only claim that resistors are in series if they do not have a node inbetween them.
    ---R1----R2---- Resistors 1 and 2 are in series

    ---R1---R2---- Resistors 1 and 2 are NOT in series
    ''''''''''''''|
    '''''''''''''R3
    '''''''''''''|

    That is however the correct approach for circuit 4.
     
  8. Apr 12, 2010 #7
    Okay, So I see what your saying. The correct answer would be E. I and IV, unless I've got something wrong out of your explanations...
     
Share this great discussion with others via Reddit, Google+, Twitter, or Facebook