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Problem graphing Irradiance and distance experiment

  1. Jan 10, 2017 #1
    1. The problem statement, all variables and given/known data
    Used a solar cell and a ray box, altering the distance from the solar cell to the light source in 10cm increments.
    Did the usual high school experimental controls and repeats.
    Assuming that the voltage is proportional to the irradiance, I am meant to graph the results.

    2. Relevant equations

    I1d12=I2d22

    I = k / d^2

    3. The attempt at a solution

    I graphed the results:
    http://imgur.com/a/Pc70V


    But as you can see, the inverse square graph isn't a straight line and I dont know why. Could it be my results or am I graphing it wrong?


     
  2. jcsd
  3. Jan 10, 2017 #2

    berkeman

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    Staff: Mentor

    What did you get when you turned the light source off?
     
  4. Jan 10, 2017 #3
    I removed as much background light as I could so the base reading was 0V, I checked that it returned to 0V between each distance when the light source was off
     
  5. Jan 10, 2017 #4

    berkeman

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    Staff: Mentor

    Can you say more about your "light box"? How well were reflections attenuated?
     
  6. Jan 10, 2017 #5
    I don't know, it's just an average high school ray box with no filter or slits attached. So it's not a point light source
     
  7. Jan 10, 2017 #6

    berkeman

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    Staff: Mentor

    Can you post a picture or a drawing? Can you see how there might be multiple paths that the source light can take to get to your detector (via reflections)? Would something like that lead to less than the ideal drop-off as you got farther away? If so, how?
     
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