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Homework Help: Measuring distances with diffraction experiment

  1. Feb 19, 2013 #1
    1. The problem statement, all variables and given/known data

    The individual threads in a cloth are very close together.
    Design an experiment to investigate how the rate at which water passes through the material depends on the separation of the individual threads in the material.

    Available equipment:
    Ammeter,battery,cloths,wires,funnel,large tank of water,low power laser,measuring cylinder,metre rule,oscilloscope,screen,top pan balance,umbrella,voltmeter

    2. Relevant equations


    3. The attempt at a solution

    So I know how to measure the distance between the cloth via diffraction, with the laser light using the interference patterns. What I actually want to know is how the ammeter,voltmeter and oscilloscope actually fit into this.

    Best I could think of is that they are used to regulate the power flowing into the laser to keep it constant?

    Also in measuring the water, why would you need a top pan balance if you can measure the water with a measuring cylinder? So wouldn't the weight of the water be irrelevant?
  2. jcsd
  3. Feb 19, 2013 #2


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    Staff: Mentor

    Similar to the umbrella, I don't think you need them (if you know how to operate the laser) - you can just pick what you need.
  4. Feb 19, 2013 #3
    But if we had to include those things: voltmeter,ammeter etc. where would they be placed, what would be their use?
  5. Feb 19, 2013 #4


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    Staff: Mentor

    Potential uses of voltmeter and amperemeter I can see:
    - Use the voltmeter to check the voltage of the battery. Compare it with the laser specifications.
    - Put equipment on top of them, if that position is better for the actual experiment.
    - Use them as weight to fix other equipment
    - Use them to heat the room
    - Trade them in exchange for more useful tools
    - Use battery, volt- and amperemeter to measure the resistance of water (from one side to the other, for example) in the measuring cylinder. Use this value to calculate the amount of water inside (after calibrating the whole method with the measuring cylinder?).
    - Disassemble to oscilloscope (dangerous!) to get electromagnets. Use them to build a simple scale, and determine the amount of water in the measuring cylinder.
    - Measure the resistance of the cloths to evaluate the possible density, assuming all probes are made out of the same material.
    - More speculative: Remove the insulation of two metal wires, put a probe of cloth on top of one of them and pull the tip of the other along the cloth material. Measure current flow between them with the oscilloscope, count the number of peaks observed (corresponding to holes in the material). Measure the linear distance of the probed region, calculate the density.

    How to use the umbrella? Well, it could be useful if the experiment is done outside in the rain.
  6. Feb 19, 2013 #5
    A paperweight, perfect!
    lol, thanks for the help though, good to know that the apparatus is as useless as I thought. Just needed to verify. The fact that the umbrella was included in addition to the cloth itself made me begin to wonder, now I can confirm.thanks.
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