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the Microscope

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    الصورة الرمزية جوهرة المحيط
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     وسام الشكر

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    تاريخ التسجيل: Sep 2006
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    the Microscope

    the Microscope

    PowerPoint on the Microscope (click to advance frames)
    Types of Microscopes
    Light Microscope - the models found in most schools, use compound lenses and light to magnify objects. The lenses bend or refract the light, which makes the object beneath them appear closer.
    Stereoscope - this microscope allows for binocular (two eyes) viewing of larger specimens. (The spinning microscope at the top of this page is a stereoscope)
    Scanning Electron Microscope - allow scientists to view a universe too small to be seen with a light microscope. SEMs donÕt use light waves; they use electrons (negatively charged electrical particles) to magnify objects up to two million times.
    Transmission Electron Microscope - also uses electrons, but instead of scanning the surface (as with SEM's) electrons are passed through very thin specimens .
    Parts of the Microscope
    1. eyepiece-where you look through to see the image of your specimen.
    2. body tube-the long tube that holds the eyepiece and connects it to the objectives.
    3. nosepiece-the rotating part of the microscope at the bottom of the body tube; it holds the objectives.
    4. objective lenses-(low, medium, high, oil immersion) the microscope may have 2, 3 or more objectives attached to the nosepiece; they vary in length (the shortest is the lowest power or magnification; the longest is the highest power or magnification).
    5. arm-part of the microscope that you carry the microscope with.
    6. coarse adjustment knob-large, round knob on the side of the microscope used for focusing the specimen; it may move either the stage or the upper part of the microscope.
    7. fine adjustment knob-small, round knob on the side of the microscope used to fine-tune the focus of your specimen after using the coarse adjustment knob.

    8. stage-large, flat area under the objectives; it has a hole in it (see aperture) that allows light through; the specimen/slide is placed on the stage for viewing.
    9. stage clips-shiny, clips on top of the stage which hold the slide in place.
    10. aperture-the hole in the stage that allows light through for better viewing of the specimen.
    11. diaphraghm-controls the amount of light going through the aperture.
    12. light or mirror-source of light usually found near the base of the microscope; the light source makes the specimen easier to see.

    Magnification
    Your microscope has 3 magnifications: Scanning, Low and High. Each objective will have written the magnification. In addition to this, the ocular lens (eyepiece) has a magnification. The total magnification is the ocular x objective
    Magnification Ocular lens Total Magnification
    Scanning 4x 10x 40x
    Low Power 10x 10x 100x
    High Power 40x 10x 400x

    General Procedures
    1. Make sure all backpacks and junk are out of the aisles.
    2. Plug your microscope in to the extension cords. Each row of desks uses the same cord.
    3. Always start and end with the Scanning Objective. Do not remove slides with the high power objective into place - this will scratch the lens!
    4. Always wrap electric cords and cover microscopes before returning them to the cabinet. Microscopes should be stored with the Scanning Objective clicked into place.
    5. Always carry microscopes by the arm and set them flat on your desk.
    Focusing Specimens
    1. Always start with the scanning objective. Odds are, you will be able to see something on this setting. Use the Coarse Knob to focus, image may be small at this magnification, but you won't be able to find it on the higher powers without this first step. Do not use stage clips, try moving the slide around until you find something.
    2. Once you've focused on Scanning, switch to Low Power. Use the Coase Knob to refocus. Again, if you haven't focused on this level, you will not be able to move to the next level.
    3. Now switch to High Power. (If you have a thick slide, or a slide without a cover, do NOT use the high power objective). At this point, ONLY use the Fine Adjustment Knob to focus specimens.
    4. If the specimen is too light or too dark, try adjusting the diaphragm.
    5. If you see a line in your viewing field, try twisting the eyepiece, the line should move. That's because its a pointer, and is useful for pointing out things to your lab partner or teacher.
    Drawing Specimens
    1. Use pencil - you can erase and shade areas
    2. All drawings should include clear and proper labels (and be large enough to view details). Drawings should be labeled with the specimen name and magnification.
    3. Labels should be written on the outside of the circle. The circle indicates the viewing field as seen through the eyepiece, specimens should be drawn to scale - ie..if your specimen takes up the whole viewing field, make sure your drawing reflects that.
    Example:


    Making a Wet Mount
    1. Gather a thin slice/peice of whatever your specimen is. If your specimen is too thick, then the coverslip will wobble on top of the sample like a see-saw, and you will not be able to view it under High Power.
    2. Place ONE drop of water directly over the specimen. If you put too much water, then the coverslip will float on top of the water, making it hard to draw the specimen, because they might actually float away. (Plus too much water is messy)
    3. Place the coverslip at a 45 degree angle (approximately) with one edge touching the water drop and then gently let go. Performed correctly the coverslip will perfectly fall over the specimen.
    How to Stain a Slide
    1. Place one drop of stain (iodine, methylene blue..there are many kinds) on the edge of the coverslip.
    2. Place the flat edge of a piece of paper towel on the opposite side of the coverlip. The paper towel will draw the water out from under the coverslip, and the cohesion of water will draw the stain under the slide.
    3. As soon as the stain has covered the area containing the specimen, you are finished. The stain does not need to be under the entire coverslip. If the stain does not cover as needed, get a new piece of paper towel and add more stain until it does.
    4. Be sure to wipe off the excess stain with a paper towel.
    Cleanup
    1. Store microscopes with the scanning objective in place.
    2. Wrap cords and cover microscopes.
    3. Wash slides in the sinks and dry them, placing them back in the slide boxes to be used later.
    4. Throw coverslips away.
    Troubleshooting
    Occasionally you may have trouble with working your microscope. Here are some common problems and solutions.
    1. Image is too dark!
    Adjust the diaphragm, make sure your light is on.
    2. There's a spot in my viewing field, even when I move the slide the spot stays in the same place!
    Your lens is dirty. Use lens paper, and only lens paper to carefully clean the objective and ocular lens. The ocular lens can be removed to clean the inside.
    3. I can't see anything under high power!
    Remember the steps, if you can't focus under scanning and then low power, you won't be able to focus anything under high power.
    4. Only half of my viewing field is lit, it looks like there's a half-moon in there!
    You probably don't have your objective fully clicked into place.

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    ahl2006
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    aissa1
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