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Improvised Optics Lab Equipment

  1. Sep 6, 2011 #1
    I'm an astronomy teacher on a very tight budget. Before I really get into the meat of astronomical information, I want to make sure that my students have some understanding of WHY it is that we know what we do about astronomical bodies, and that means getting them to work with some of the tools and principles that astronomers use, like the light gathering ability of optical components, the dispersion of luminous energy at a distance, basic optical set-ups, and some basic spectroscopy.

    I've identified quite a bit of equipment that I need in order to do experiments with these topics. This list is:

    An optics bench (basically a yardstick with clasps to hold lenses/mirrors/screens/etc.)
    Lenses
    Mirrors
    Spectroscopes
    Spectroscopy gas samples in tubes
    The electrical apparatus to excite the samples
    Light sensors and interface equipment (just something to measure the intensity of light for an inverse-square-law basic experiment)

    Now, last year I had students build their own spectroscopes with peeled cds as a diffraction grating and cardboard tubes. They worked reasonably well.

    I'm looking for ways that I can provide improvised equipment. Some method of quantitatively measuring the intensity of light to explore the inverse-square law. Some way of either creating my own gas samples or building my own device to excite the gases to the point of luminescence.

    I feel that the optics bench is probably where I'll get the most bang for my buck, so that's what I've planned to buy so far, but if people disagree, I might reconsider.

    Educations are at stake!
    Help me, Physics-Forums Kenobi.
    You're my only hope.
     
  2. jcsd
  3. Sep 7, 2011 #2
    I'm not sure about the gas samples (are you trying to make emission lines? How about street lights, neon signs, LEDs and the like?), but I've had good luck just shopping at educational-type stores. You can find cheap lenses and mirrors, diffraction grating film (bound to work much better than a CD), prisms, etc. - I actually built a dirt-cheap prototype rotary interferometer using this sort of stuff, wrapping grating film around a cut glass cylinder, and also a cheap liquid-crystal laser beam deflector. And this was for a company I was working for, not for students. ;-) For intensity measurements, it's hard to beat a photocell - you could build something yourself using components, if you have something like an oscilloscope to display the output, or you could find an old photography light meter. Edmund Scientific used to be a great source for cheap/surplus optics-related stuff, not sure if it still is.
     
  4. Sep 7, 2011 #3

    Andy Resnick

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    I appreciate what you are trying to do. My recommendations assume you are paying for everything out-of-pocket, and thus the idea is to spend as little as possible.

    I'll take an opposite position from you- since you are not going to be doing experiments that require a high degree of accuracy or precision, an optics bench may not be the best use of your funds- you could probably get by with a sheet of 3/4" thick plywood placed on top of a partially inflated inner tube/cinder block/hockey pucks, placed within a sand pit.

    For an inverse square-law measurement, I suspect an incandescent lightbulb and a photovoltaic cell would be sufficient. If you want to show spectral lines, a fluorescent bulb, sodium lamp, metal halide, or other standard lamp could be used. Oftentimes LED companies will send you small kits for free if you explain who you are and what you are trying to do (I have one from Lumix- lots of LEDs, a few diode lasers- all can be powered by a AA battery)

    Good luck!
     
  5. Sep 7, 2011 #4
    Hello Lumen.Reading your post triggered a memory of a very cheap but nevertheless reasonably effective device called the "grease spot photometer".The main part of the photometer is literally a spot of grease added to some paper.You can make one in seconds by dipping a finger into something like vegetable oil and then touching your finger to the middle of a sheet of paper.
    You will need other bits and pieces such as one or more measuring rulers and a lamp and other light source(s).The whole thing can be put together very cheaply.A google search should give you the details you need.
     
  6. Sep 8, 2011 #5
    Update: while I find the grease spot photometer to be awesome, I just did some scrounging in the depths of the science closet at my school. Just turned up some basic photometers and some nice spectroscopes as well as a couple chemical spectrophotometers (though I'm not sure I can use these).

    I'll try asking Lumex or another LED manufacturer for some samples of their stuff. I'm hesitant about it, though, because I'm not really sure what process makes a LED generate its light. I know that in astronomy, we're only really concerned about blackbody radiation continuous spectra and the emission or absorption lines created by clouds of gas over vast distances. I've looked through a spectroscope at LEDs and I've seen what looks like an emission spectrum. I don't know if it's accurate, though because I don't really see how the same process could be working on the semiconductor in the LED. If someone can help with that, it could solve all my problems (since it would leave only one type of equipment to buy).

    Alternatively, I've gotten my hands on some cannisters of gases from the chemistry department in my school, but I'm not sure how to turn this into something that will generate emission lines. Something about particular voltages ionizing the stuff. Not sure I fully understand the electrical parts of this. Ideas?
     
  7. Sep 8, 2011 #6

    xts

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    Photometer: you may utilize any photoresistor or photodiode (both below $1.00, or may be picked from electronics junk), battery and mA-meter. You must callibrate it, but that's another good excercise for your pupils.

    Gas lines - that's not that easy at very low budget. You must decompress the gas to low (0.01 atmosphere) pressure in a glass pipe with electrodes. For my experience - not that easy at very low budget.
    You may try with emission lines (or even absorption lines) of elements in a flame excitation: take a Bunsen's gas burner, and put small samples ov various elements. Sodium, Barium, Calcium, Strontium, Copper - all works very fine, many other elements may also be tested.

    If some of your pupils have (even cheap) digital photo cameras - that's a perfect tool for cost-free school astronomy. You may use it as a photometer (for relative measurments), pretty precise tool to record angles between celestial objects, etc.
     
  8. Sep 8, 2011 #7
    Those gas samples are at a low pressure? I suppose that makes sense. Is it just that you're heating up the gas, but it's not generating a continuous spectrum because it's not dense enough to do so?
     
  9. Sep 8, 2011 #8

    xts

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    Yes, they are usually at 0.01 or even 0.001 bar. Sharp spectrum is not the only reason for making them low-pressure, see:
    http://en.wikipedia.org/wiki/Gas-filled_tube,
    http://en.wikipedia.org/wiki/Gas-discharge_lamp

    ADDED>
    But you may buy cheap (or find at junk...) such noble gas lamps, used as indicators in old-fashioned electronics. Neon lamps were most common, but other may also be found. Such lamps may be excited by 240VAC through some (10 kohm or so) resistor.
     
  10. Sep 8, 2011 #9

    Andy Resnick

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    doh! I should have thought of that- camera phones are ubiquitous and extremely useful- good call.
     
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