How can I get the voltages???

Discussion in 'Homework Help' started by wheeltiger, Aug 30, 2007.

  1. wheeltiger

    Thread Starter New Member

    Mar 19, 2007
    6
    0
    :(I have built a RLC circuit with a capacitor parallel to 2 resistors and an inductor.
    I have measured the voltages through the oscilloscope with:
    Ch1 at the voltage source to ground
    Ch2 at the end of the inductor to ground
    Ch3 at the end of 1 resistor that is parallel to the capacitor to ground

    How can I work the the voltages across the resistor and inductor?:confused:

    Please help!!!:confused:
     
  2. hgmjr

    Moderator

    Jan 28, 2005
    9,030
    214
    Can you please draw and post the circuit?

    It is much easier to discuss a circuit when a clearly labeled diagram/schematic is involved.

    As this is a problem that has been assigned for you to solve, the forum members are generally reluctant to blurt out the answer. They are however good at providing hints and suggestions intended to lead you to the solution so that you to do most of the work.

    The more you can show that you have made an attempt to solve the problem, the more sympathy you will receive. Many if not most of the experience members have encountered the same confusion and endured the angst you are feeling toward problems just like the one you are trying to learn.

    hgmjr
     
  3. wheeltiger

    Thread Starter New Member

    Mar 19, 2007
    6
    0
    Thanks, :)
    Here is the circuit:


    I used Kirchoff's Voltage Law and get 2 formulae for Right hand side loop and Left hand side loop:
    RHS: (I1).(L1) + (I1).(R2) - (I2).(R2) + (I1).(R1) = V1
    LHS: (I2).(R2) + (I2).(C1) - (I1).(R2) = 0
    Then, I used Cramer's rule to solve for I's.
    Then, I used V = I.Z to work out each of the voltages...
    Is this correct???:confused:

    :(But I think I am suppose to do something with the measured voltages...
    but I don't know what I need to do with them...

    Thanks :)
     
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  4. hgmjr

    Moderator

    Jan 28, 2005
    9,030
    214
    A couple of question for you.

    1. Is your task to find the total voltage drop across the resistor R1 and the inductor L1?

    2. Are you being asked to provide the answer as an expression in the time domain form or the frequency domain form?

    hgmjr
     
  5. techroomt

    Senior Member

    May 19, 2004
    198
    1
    if you want to truly measure across a component that is not grounded at one end, then you must break the ground level that the o-scope has through the 3 prong power/grounded plug, with a 3 into 2 adapter and the little tab not touching the cover screw. with the ground broken, you can now attach the scope (floating) ground with a jumper to one end of the component and the probe to the other end. i do this on a regular basis.
     
  6. hgmjr

    Moderator

    Jan 28, 2005
    9,030
    214
    Exercise caution in defeating the third wire ground as there is a level of risk of getting shocked if you are not careful.

    hgmjr
     
  7. wheeltiger

    Thread Starter New Member

    Mar 19, 2007
    6
    0
    :) Thanks for all replies

    I was actually told to work out the phasor currents for this circuit...
    but I was told as a hint that the voltages I measured is with reference to ground... and I was suppose to work out the separate voltages...:confused:
     
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