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Inductance issues

  1. Dec 30, 2013 #1
    1. The problem statement, all variables and given/known data
    Determine the resistance of a 0.2H coil used to replace the inductor if the circuits time constant falls to 0.55ms.


    2. Relevant equations
    l/R


    3. The attempt at a solution L/R = 0.2H/R = 0.55ms
    Transposing for R... R = 0.2/0.0055 = 36.36Ω is the resistance of the coil?
     
  2. jcsd
  3. Dec 30, 2013 #2

    rude man

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    Your English is not good so I don't know exactly what the problem is.

    If it's to find the value of R in series with a pure inductor of L = 0.2H to give a time constant of 0.55 ms then your formula is right but you misrepresented 0.55 ms.
     
  4. Dec 31, 2013 #3
    Sorry i failed to submit all the question. Here it is: An inductor of negligible resistance and an inductance of 0.2H is connected in series with a 330Ω resistor to a 12 d.c supply. Determine the resistance of a 0.2H coil used to replace the inductor if the circuits time constant falls to 0.55ms.

    yep got my powers wrong. So it will be 0.2/0.00055 = 3.6Ω?
     
  5. Dec 31, 2013 #4

    rude man

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    You have a perfect inductor L of 0.2H in series with R1 = 330 ohms and R2 with unknown resistance (to be solved).

    What is the time constant of this configuration as a function of L, R1 and R2? L, R1 and the numerical time constant are known. Solve for R2.
     
  6. Jan 1, 2014 #5
    R= 0.2/0.00055 = 363Ω is total resistance.

    resistance - 330Ω = 33.6Ω is coil resistance when the circuits time constant falls to 0.55mS?
     
  7. Jan 1, 2014 #6

    rude man

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    Right!
     
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