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Homework Help: IV curve for voltage across shunt for probe current (Helimak experiment)

  1. Mar 24, 2015 #1


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    1. The problem statement, all variables and given/known data
    Let's say I have a Langmuir probe I-V characteristic from the Helimak experiment. The plasma ions are singly ionized argon. The probe has an effective area of 0.000016 m^2. Estimate the floating potential, electron density,
    and temperature. Based only on the nature of the data itself, estimate the uncertainties in these values. This data was taken by sweeping the bias voltage at a frequency of a few Hertz and averaging over 15s to reduce the effect of fluctuations, which are still visible in the

    The first column is the voltage applied to the probe. The second is the voltage across a 5-kilo OHm shunt to measure probe current

    2. Relevant equations

    3. The attempt at a solution

    What I am confused about is that when I plotted the values given in the problem, the curve resembles an IV curve. However, since the y-values are "voltage across a 5-kilo OHm shunt to measure probe current", how would I convert this to current, and thus be able to solve for the floating potential, electron density,
    and temperature. ?
  2. jcsd
  3. Mar 28, 2015 #2


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    2017 Award

    Staff: Mentor

    Maybe I'm missing something, but what would be wrong with just using V=I*R? You know resistance and voltage across the resistor.
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