Tuning Frequency

Discussion in 'Homework Help' started by frisky, Jul 25, 2005.

  1. frisky

    Thread Starter New Member

    Jul 25, 2005
    3
    0
    I am not sure if I am doing this question right:

    A coil and 2 capacitors are connected in parallel. If the inductance of the coil is 100 uH and the fixed capacitance C1 is 80 pF, what should be C2 to tune in a broadcast frequency of 1000 kHz?

    Here is what I was thinking:

    C1 and C2 are in parallel, so their combined capacitance is C1 + C2.

    A resonant circuit has maximum current when 2πfL = 1/(2πfC), or

    C = 1/((2πf)^2L)

    Since C = C1 + C2

    C2 = 1/(2πf)^2L) - C1

    Is this right?
     
  2. hgmjr

    Moderator

    Jan 28, 2005
    9,030
    214
    Hi Frisky,

    Your equations all look good. You are obviously absorbing the material being presented.

    I think that the phrase in your post that I have highlighted in RED may be more generally stated by saying that an RLC circuit whether it is a parallel or a series configuration is said to be in resonance when 2πfL = 1/(2πfC).

    What was your final answer for the value of C2?

    Good job,
    hgmjr
     
  3. frisky

    Thread Starter New Member

    Jul 25, 2005
    3
    0

    173 pF
     
  4. hgmjr

    Moderator

    Jan 28, 2005
    9,030
    214
    That's the value I calculated when rounded to the nearest pF.

    Good work,
    hgmjr
     
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