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Homework Help: Placement of a resistor

  1. Aug 23, 2013 #1
    Am I correct in thinking that it would not matter if I place the 100ohm resistor after the 220nF capacitor (as shown in the picture), or before the capacitor?

  2. jcsd
  3. Aug 23, 2013 #2
    It certainly does matter where you place the resistor in this circuit, since each side of the capacitor has a different polarity. Furthermore, you have the 100 ohm resistor in parallel with R13, which tells me that you are trying to achieve a value for a resistance that you could not otherwise provide using a single resistor that you do not have in your possession as in Rtotal=1/(1/R1 +1/R2), which in this case is effectively 99.338 ohm, so by that reasoning alone, the resistor is improperly placed.
  4. Aug 23, 2013 #3


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    Staff: Mentor

    For a number of reasons, it probably does matter. Where it currently sits means that J "sees" an infinite DC path to ground. But move that resistor to the other side, and signal at J "sees" a DC path of 100Ω to ground. Big difference, where it's important.

    You can apply similar reasoning to what the circuit on the right sees.
  5. Aug 27, 2013 #4


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    Science Advisor
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    Gold Member

    I agree with other replies.

    It probably does matter but more information is required to fully answer the question.

    As baudrunner points out the combination of 100R and 15K in parallel is unusual. Not least because the effect of the 15k on the combined impedance is small. What is the manufacturing tolerance of the 100R? The 15K affects the impedence by less than 1% so if the manufacturing tollerance of the 100R was say 1 or 2% then you have to wonder why the 15k is there at all.

    The answer might also depend on the input frequency. Currently anything below about 7Khz is attenuated by the high pass filter (220nF & 100R).


    If you swap the 100R to the left of the 220nF that won't work the same. The corner frequency will increase to something much higher (220nF and 15k//20K).
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