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Two Frequency Input Solving for Output

  1. Feb 18, 2012 #1
    Say for example you have a Input Voltage in a circuit that is equal to Vin = 4cost + 5sin2t. Clearly, the input is operating on two different frequencies, namely w=1 and w=2. I am trying to find the Output Voltage across an arbitrary resistor in the circuit. The circuit consists of resistors and a capacitor, so its quite plain and standard.

    My question is, how do you solve for the output given the above input, considering the different frequencies? My intuitions tells me to solve using Vin=4cost first and get the Vout, then solve using Vin=5sin2t and get another value for Vout, and the actual Vout will be the sum of the two. Is that correct?
     
    Last edited: Feb 18, 2012
  2. jcsd
  3. Feb 19, 2012 #2
    If you driving a load with a voltage source like what you gave, the voltage across the load is just Vin!!!! Because you specified it is a voltage source and it has zero output impedance!!!! It does not care what load it is!!!!

    I am just trying to give you a bad time. You have not given enough info on what is the output. You need to draw the circuit. Yes, if Vin = 4cost + 5sin2t, you treat is as two separate voltage one with w=1 and the other w=2.
     
  4. Feb 19, 2012 #3
    I wasn't talking about the voltage across the TOTAL load. Read over the post again. I mentioned Vout being the Voltage across ONE arbitrary resistor in the circuit consisting of resistors(plural) and a capacitor. Thus, the voltage across the individual resistors will not equal the voltage source itself since there are other components also in the circuit. Give us newbs a hardtime, but don't forget reading comprehension!!! just giving you a hard time.

    The last part of your post answered my question. So you treat it as two seperate voltage sources. Thats what i needed. Thanks buddy!
     
  5. Feb 19, 2012 #4

    jim hardy

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    Is Superposition method stiill taught?
     
  6. Feb 19, 2012 #5

    sophiecentaur

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    Writing in a more concise way could avoid misunderstanding. If you want a proper answer to a specific question it is always a good idea to supply a diagram of the actual circuit rather than assuming you've described it unambiguously. What could "total load" possibly mean?
     
  7. Feb 19, 2012 #6
    Also he could be more graceful in replying as he is the one that need help. I started out as a friendly joke, but no matter how I read the response, that didn't sound very friendly.
     
  8. Feb 19, 2012 #7

    sophiecentaur

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    Kids these days!
     
  9. Feb 19, 2012 #8
    :rofl::rofl:
     
  10. Feb 19, 2012 #9
    I was actually taken back a little.........Is this a trick question or am I missing something? I actually went through Fourier Series etc. before I responsed!!! That's kind of got me into the joking mood!!!
     
  11. Feb 19, 2012 #10

    sophiecentaur

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    It's bang right on as the way forward isn't it? You have to work out the answer in the frequency domain and then bung it all together together to find the time function.
     
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