Calculating phase shift frequency

Discussion in 'Homework Help' started by JDR04, Aug 25, 2012.

  1. JDR04

    Thread Starter Active Member

    May 5, 2011
    339
    4
    Could somebody tell me if I am correct , or, where I went wrong please.

    I'm asked to calculate phase shift frequency. I'm given total resistance as 8 ohms and capacitance as 0.003microfarad.

    f=50/rc f=50/0.008 X 0.003 = F=50/0.00024 so f = 208333.33
    Phase shift frequency is 208.333Khz

    If somebody could tell me if I am right or wrong it would be appreciated. Thanks again -JDR04
     
  2. WBahn

    Moderator

    Mar 31, 2012
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    What is "phase shift frequency"?

    Where does the '50' come from? What does it represent? It has to have units of 'cycles'.
     
  3. JDR04

    Thread Starter Active Member

    May 5, 2011
    339
    4
    Hi WBahn, I think we talking about a RC phase shift oscillator here. All I'm given is a formula that is

    f=50/r x c. Does that help at all?
     
  4. WBahn

    Moderator

    Mar 31, 2012
    17,788
    4,807
    No. That does not help at all.

    When you say, "All I'm given ....", given by whom?

    What is it that you are supposedly learning? To plug a couple numbers into a formula that you are following blindly when you don't even know what kind of circuit you are supposedly working with? Is that the level of comprehension that is being expected? Is that the level of comprehension that you think will suffice for what you want to do with what you are supposedly learning?

    As an aside, I think you mean f=50/(rc) and not f=(50/r)c, which is what you have written.

    Order of operations counts.
     
  5. JDR04

    Thread Starter Active Member

    May 5, 2011
    339
    4
    Hi WBahn, sorry for the delayed response. Youre 100% right, I thought I did undertsand the problem but after reading your entry I realise I don't really. So, it's back to the books to see if I can improve.

    In answer to your "what I am sUpposedly studying", It was this forum that inspired me to study electronics so I decided to do a BTEC level 3 in electronics by way of correspondence to try and get a good grounding on the subject. However I will take your comments in a positive light as I have learnt something from it and I thank you for it.

    Thanks again - JDR04
     
  6. WBahn

    Moderator

    Mar 31, 2012
    17,788
    4,807
    They were meant as constructive feedback, but upon re-reading them I can see how that may not be apparent. I'm glad you chose to interpret them as such.

    After you've pondered the problem a bit, repost a more complete question. Perhaps posting the entire problem will help establish the necessary context for us to fill in any remaining gaps.
     
  7. ldavey44

    New Member

    May 8, 2014
    2
    0
    Hello everyone, sorry to re-open this old thread but it looks asthough I am doing the same course as JDR04 (although he must have finished this by now.)

    I am stuck on the same question and it is the only question preventing me from handing in my 2nd Assignment.

    For JDR04 - Only difference in my question they ask for resistance of 8 kOhms not Ohms. Below is what I have calculated but the course is just not sufficient on explaining things to fully understand.

    1) Calculate RC = R x C = 8 x 0.03 = 0.24
    2) 50/ 0.24 = 208.33333333333333333333333333333
    Phase Frequency = 208.33 Hz

    I noticed you put Khz but my answer is in Hz due to the kOhms - is 208.33 the same answer you finally used before submitting?
     
    Last edited: May 8, 2014
  8. Veracohr

    Well-Known Member

    Jan 3, 2011
    552
    76
    If the question is referring to a phase shift oscillator like this:

    [​IMG][​IMG]

    The equation is wrong. Google it and you'll find the equation quickly.

    Your calculation of RC is wrong too. 8*.03 is not the same as 8000*.000000003.
     
  9. ldavey44

    New Member

    May 8, 2014
    2
    0
    Sorry for taking so long to reply. I have found myself unexpectedly unwell. Because of this I sent my assignment off without any amendment.

    Good news is I passed the module so my answer must have been correct but I still do not know totally understand why lol.

    I will dig out and scan in an oscillator drawing from the course when I can because I would like to understand all this.

    Thanks for the reply Veracohr, I appreciate the help.
     
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