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Homework Help: Intensity of light / measuring wavelength of light

  1. Apr 30, 2007 #1


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    Hi! I am an English AS-level Physics student. I am stuck with my planning exercise and I thought these forums would be a good place to find some other people who are having similar problems, and perhaps we can work something out together.

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

    "You are required to design a laboratory experiment using a ligh dependent resistor (LDR) to investigate how the intensity of light emitted by a lamp varies with wavelength."

    "...in your account you should pay particular attention to..

    A) the procedure to be followed

    B) how the wavelength of the light falling on the LDR is determined

    C) how a measure of the intensity can be obtained from the LDR

    D) the range and precision of any intruments that would be used

    E) the factors that would need to be controlled to ensure that it is a valid test

    F) any safety precautions you would take when carrying out the investigation

    G) particular features of the design that would ensure the accuracy and reliability of your results."

    2. Relevant equations

    I think Lambda (wavelength) = ax / D is relevant, as a two-slit interference experiment could find the wavelength of the light.

    Intensity = power / area ? I think this formula is correct but I am unsure!

    3. The attempt at a solution

    I think using coloured filters to block out certain wavelengths could be used around the LDR, to make sure only certain a wavelength of light is acting on the LDR.
    I also think the above formula could be useful in finding out this wavelength

    I do not know much at all about LDRs, and I do not know how they can be used to measure how wavelength interferes with intensity. I am also unsure about the formula for intensity.

    I appreciate any tips or help you guys can give me on this, I really am stuck on what to do!

    I hope this is one of many posts on this forum.

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

    2. Relevant equations

    3. The attempt at a solution
  2. jcsd
  3. Apr 30, 2007 #2
    I think a two-slit approach would not be practical and even maybe not feasible.
    Maybe, you should read about diffraction gratings and monochromators and maybe also about the optical prisms.
  4. Apr 30, 2007 #3


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    I may only use standard equipment to plan this practical. A monochromator sounds like it would work, but I don't think it is part of the equipment I would be expected to use.

    What about if I surrounded the LDR with a filter so that only one colour (and thus wavelength) of light could effect the LDR? I could change the filter to allow me to measure different wavelengths effects.
    If that would work, I'd just need to work out about intensity...

    Thanks a lot for your reply though mate! I'll see what my classmates think about the use of a monochromator.
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