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Lab 4

  1. Feb 18, 2009 #1
    1. The problem statement, all variables and given/known data

    well first its to plot the graph ( volt vs. current) then determine the effective resistance of the two resistors in series. 2nd compare the effective resistance of the resistors in series with the resistances of each resistors.

    2. Relevant equations

    R=V/I

    3. The attempt at a solution
    Based on this chart: then graph
    Voltage (Volts) Current (Amps)
    3.24 .021
    9.32 .060
    14.67 .095
    20.3 .123
    8.2 .056
    15.4 .106



    R= V/I 3.24/.021 = 154.3
    15.4/.106 = 145.3
     
    Last edited: Feb 18, 2009
  2. jcsd
  3. Feb 18, 2009 #2

    Tom Mattson

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    That sentence makes no sense at all. Can you please carefully type out the problem exactly as it appears in your lab handout?
     
  4. Feb 18, 2009 #3

    djeitnstine

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    I assume you mean "effective resistance of 2 resistors in a series circuit" in which case you simply add them up
     
  5. Feb 18, 2009 #4

    Tom Mattson

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    Sure, that's how you compute them. But the OP says compare. What is he supposed to compare them to? :confused:
     
  6. Feb 18, 2009 #5
    well first its to plot the graph ( volt vs. current which i did) then determine the effective resistance of the two resistors in series. 2nd compare the effective resistance of the resistors in series with the resistances of each resistors.
     
    Last edited: Feb 18, 2009
  7. Feb 18, 2009 #6

    Tom Mattson

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    OK, so do you know how to get the effective resistance from the plot of voltage vs current?
     
  8. Feb 18, 2009 #7
    pick 2 coordinate points and find slope, where slope = R
     
  9. Feb 18, 2009 #8

    Tom Mattson

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    I wouldn't just pick 2 points, but rather the best line that fits all of the data. If you haven't learned about that (linear regression that is) then I would just compute the resistance for each data point and then average them. That will be the effective resistance.
     
  10. Feb 18, 2009 #9
    can u pick 2 point from graph on the line and find slope? then once you find the effective resistance, then compare the effective resistance of the resistors in series with the resistances of each resistors?
     
  11. Feb 18, 2009 #10

    Tom Mattson

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    Like I said, I wouldn't pick just two points. If you do that then you aren't taking all of the data into account.
     
  12. Feb 18, 2009 #11
    but in general to find resistance using ur data points do u do V/I = R or v2-v1/I1-i2 for a single resistor?
     
  13. Feb 18, 2009 #12

    Tom Mattson

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    Only if you have 2 data points. If you have more then they must be included somehow.
     
  14. Feb 18, 2009 #13
    If I have this
    Data Table 2: The Voltage vs. Current for a Single Resistor Circuit
    Current V
    0.01 0.5
    0.02 0.8
    0.03 1.3
    0.04 1.8
    0.05 2.3


    then would i calc. (2.3- 1.3)/ (.05-.03) = 50
     
  15. Feb 18, 2009 #14

    Tom Mattson

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    Can't you see that if you use only those two data points that you're ignoring the rest of the data?
     
  16. Feb 18, 2009 #15
    so i have to calculate each indivudual points?
     
  17. Feb 18, 2009 #16

    Tom Mattson

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    I said that 8 posts ago. :rolleyes:
     
  18. Feb 18, 2009 #17
    Resistances

    1. The problem statement, all variables and given/known data

    well first its to plot the graph ( volt vs. current)
    then
    1. determine the effective resistance of the two resistors in series.
    2nd compare the effective resistance of the resistors in series with the resistances of each resistors.

    2. Relevant equations

    R=V/I

    3. The attempt at a solution

    Based on this chart: then graph
    Voltage (Volts) /Current (Amps)
    3.24 /.021 =154.3
    9.32 /.060 = 15.53
    14.67 /.095 = 154.4
    20.3 /.123 =165.0
    8.2 /.056 =146.4
    15.4 /.106 = 145.3


    I divided (v/I = r)

    so far I dont know how to continue.
     
  19. Feb 18, 2009 #18

    Tom Mattson

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    I've merged your two threads. In the future please do not start multiple threads for the same question. It is not necessary and is considered spam.

    I told you exactly how to continue in Post #8.
     
  20. Feb 18, 2009 #19
    so for series i calculate each individual then add all the R's and get the average, is it the same for parallel too?
     
  21. Feb 18, 2009 #20

    Tom Mattson

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    Yes, I would do the same for parallel resistance.
     
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