elementary questions on capacitance

Discussion in 'Homework Help' started by electronicstech07, Sep 23, 2008.

  1. electronicstech07

    Thread Starter Member

    Nov 16, 2007
    18
    0
    I am having some problems understanding what I am reading on the subject of capacitance. The first is temperature coefficient. The question in my textbook is asking a 2 uF capacitor has a positive temperature coefficent of 50 ppm/C, what is the capacitance when the temperature increases by 100 degree C.

    I understand that positive temp. coefficent means the capacitance will increase per degree C increase, but can't seem to calculate the right answer. How exactly do I calculate this?


    The next question is to obtain a reactance of 2 kil ohm from a 0.1 uF capacitor, what frequency is required? How can I calculate this?

    Help is greatly appreciated!
     
  2. scubasteve_911

    Senior Member

    Dec 27, 2007
    1,202
    1
    Hey,

    So, if temperature increases by a degree celcius, the capacitor will increase its capacitance by 50 parts per million. So,

    C(100degrees) = Cnominal(1 + 100 * 50 * 10^-6)
    C(100degrees) = 2.01uF

    Xc = 1/(2*pi*f*C)

    Solving for f

    Xc(2*pi*f*C) = 1
    f = 1/(2*pi*C*Xc)
    f = 795.77 Hz

    Steve
     
  3. electronicstech07

    Thread Starter Member

    Nov 16, 2007
    18
    0
    That cleared up the confusion. Thanks again!
     
  4. scubasteve_911

    Senior Member

    Dec 27, 2007
    1,202
    1
    You're welcome sir,

    I'm just glad you didn't mean 'elementary' as in calculating capacitance from electromagnetics principals :p

    Steve
     
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