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Homework Help: Ac Electronics

  1. Sep 29, 2005 #1
    :cry: hi i got 2 questions here fairly confusing was wondering if i can get some help thanks

    1. consider a series RLC circuit in which R is an incandescent Lamp C is some fixed capacitor and L is a variable inductance. The source is 240 V ac.
    explain why the lamp glows brightly for some values for L and does not glow at all for other values

    * not sure about this question but i am thinking along the lines that when capacitor discharge current + power source current = inductor current
    when there is no current flow bulb wont glow can someone provide me with a better explanation thanks

    2. an inductor is connected to a sinusoidal voltage with amplitude of 120V. A peak current of 3.0A appears in the inductor.

    a)what is the maximum current if the frequency of the applid voltage is douled
    b) what is the inductive reactance at each of the two frequencies?

    * i know Vmax=120 i have the equations il=imaxsin(wt - pi/2)
    and imax = Vmax / Xl whre Xl=wL
    any ideas how to approach this question i tried using Imax=3 not working heh
  2. jcsd
  3. Oct 1, 2005 #2


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    Homework Helper

    1. The lamp will glow brightly when the current in the circuit is large, which will be the case when the total AC resistance of the circuit (the impedance) is small. The impedance of a series RCL circuit depends on the square of the difference between the reactances (AC resistances) of the capacitor and the inductor. If these two reactances is the same (a certain choice of L) the difference will be zero giving a small impedance and resulting large current in the series RCL circuit.
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