RC Circuit Question - Inductive Reactance = Impedance?

Discussion in 'Homework Help' started by free1, Oct 5, 2011.

  1. free1

    Thread Starter New Member

    Oct 5, 2011
    We just simulated a circuit in lab with a 100ohm resister connected to a 33mH inductor in series. It was powered by an oscillator supplying a steady 4vp-p. The point of the experiment was to change the frequency from 200hz-10000hz and monitor how frequency affects the inductor. One thing I cannot figure out though is why the inductive reatance equals the impedance of the circuit at 5000hz? Should the impedance also equal the inductive reatance at 200hz as well? If so, why? At 200hz the impedance and inductive reactance are very close but not equal. Any help is greatly appreciated. I am just starting to learn circuit analysis so please be patient with me. I am sure this is something simple but I just cannot figure it out.
    Last edited: Oct 5, 2011
  2. Adjuster

    Well-Known Member

    Dec 26, 2010
    The total impedance will always include contributions from the coil and the resistor, but at higher frequencies the inductive reactance is greater, and so makes up a greater proportion of the total. This effect is reinforced by the fact that reactance and resistance in series add like two sides of a right triangle, where the impedance is represented by the hypotenuse.

    If you calculate the reactances of the coil at different frequencies using XL = 2∏fL , and (magnitude of) Z=√(R^{2} + XL^{2}) you should see what is happening.

    I suppose it is just possible that the coil's parasitic self-capacitance may be affecting things at the higher frequencies.
    Last edited: Oct 5, 2011