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Homework Help: Light dependent resistor experiment!

  1. Mar 29, 2009 #1
    1. The problem statement, all variables and given/known data

    Hi there I never managed to get a decent set of results in my physics coursework as I was unfortunately ill for the last few lessons of experiment time! My teacher won't let have an extension and won't let me do any more experimenting during lunch hours!
    Basically by using an LDR I was looking at how the depth of water effect the resistance of the LDR (by measuring current) and hence finding out how depth of water affected the amount of light absorbed by the water. I know that obviously that the deeper the water is the the more light will be absorbed meaning the resistance of the LDR will be greater as less light will pass through the water however: I'm unsure as too whether the amount of light absorbed by the water is directly proportional to the depth or not. Could anyone help me......I did manage to get some results which suggested that as the water got deeper the rate at which light was absorbed decreased (as the water got deeper the difference in current between each depth decreased.)

    2. Relevant equations Ohm's law I=V/R comes into play, I am using a power pack to supply a constant 3 volt voltage to the circuit. So as resistance due to light absorption changes the current will also change.

    3. The attempt at a solution

    I think I've already outlined my attemt, it's simply I didnt have enough time to complete my experiment as enough different depths to draw an accurate conclusion to how light absorption is affected by depth, so was wondering if anyone on here could help??
  2. jcsd
  3. Mar 29, 2009 #2


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    Welcome to PF.

    The amount of light should follow an exponential decay law, as depth is increased.
  4. Mar 30, 2009 #3
    Thank you! Very helpful of you, couldnt find any information online anywhere!
    Last edited: Mar 30, 2009
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