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Homework Help: How to find supply frequency of an AC circuit

  1. Jan 13, 2015 #1
    1. The problem statement, all variables and given/known data

    Parallel circuit consists of 100ohm resistor with 0.4A current, a 0.47uf capacitor with 0.177A current. Both connected across an AC supply, determine

    2. Relevant equations

    The supply voltage
    The supply frequency
    Current drawn from supply
    Power factor of the circuit
    The Apparent power

    3. The attempt at a solution

    The supply voltage is 40V.
    Supply frequency is where im stuck at the minute. I have VL=VC=XC

    So VC=1/(2PiFC)
    Substitute F for VC and I get VC=1/(2PiC*VC)
    F= 1/(2Pi *0.47x10-6*40V)
    Doing that equation I get 8465.69Hz which is crazy?

    Thanks in advance Alan
    Last edited by a moderator: Jan 13, 2015
  2. jcsd
  3. Jan 13, 2015 #2


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    Hello Alan, welcome to PF :)

    Do the relevant equations look like equations to you ?

    I take it the 40 V follows from I = V/R, so that qualifies as an equation and you have attempted a solution (and it's OK)

    Perhaps the 0.177 and the 0.47 uF plus the 40 V can lead you to a frequency -- if you have a decent equation at hand, that is. Any idea ?

    PS Check out the guidelines
  4. Jan 13, 2015 #3


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    Staff: Mentor

    Hello Alan,

    Welcome to Physics Forums.

    Voltage and reactance are not the same thing (one has units of Volts and the other Ohms). You have the potential across the capacitor (40 V) and the current though it, so you can determine the reactance...
  5. Jan 13, 2015 #4
    This is where Im at now, Xc=V/I wich is 40V/0.177A=225.99

    F= 1/(2Pi * 0.47x10-6 * 225.99)= 1498.41Hz
  6. Jan 13, 2015 #5


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    Well done
  7. Jan 12, 2018 #6
    How to calculate frequency of AC signal?
  8. Jan 12, 2018 #7


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    Hello Sanat, :welcome:
    Please start a new thread for this question and use the homework template.
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