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Homework Help: Measuring output of LDR

  1. May 12, 2007 #1
    1. The problem statement, all variables and given/known data
    it is a reasearch project i have to plan an experiment to find what effect different wavelengths of light, from a lamp which is used to grow plants, will have on the output of an LDR.

    2. Relevant equations

    3. The attempt at a solution

    so far my plan is (breifly) to use a lamp and put coloured filters in front of it to controll the wavelength. also i have researched a CdS cell which would be the standard lab LDR i will use. The only thing i really need help with is a proximate ranges for meters required. as i have bin looking for days and cant find anything that would help, i am using an ammeter and voltmeter to give the power output. "P=VI"
  2. jcsd
  3. May 12, 2007 #2


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    The distance between light source and LDR (light dependent resistor) would determine the number of photons arriving at the LDR, by virtue of the area * photon flux.

    One could start some distance away from the light source and gradually move the LDR closer and measure the response or signal strength.

    This might provide some insight - http://www.doctronics.co.uk/ldr_sensors.htm [Broken]

    The filtering will also affect the flux since it will 'filter out' some fraction of the photons. It would perhaps be better to place the filter nearer to the detecting LDR rather than the source.
    Last edited by a moderator: May 2, 2017
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