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Main Title

Building a
Microscope and
Identifying Cells

Box of Lenses Brother Gregory has just received a box of microscope slides prepared by his old Professor at the University of Vienna. Herr Professor Ausbach needs his help identifying all the various types of cells on these microscope slides, and has asked Brother Gregory look at them.

Unfortunately, while getting his valuable microscope out of it's box, Brother Gregory dropped it on the floor!

Now the microscope is in pieces and all Brother Gregory has left is a box of old microscope lenses. He doesn't even know what kind of lenses they are, what type of glass they are made of, or what kind of magnification they will provide.

Help Wanted Brother Gregory wants you to help him find out what kind of lenses are in the box, use these lenses to rebuild a microscope, and then examine and identify the cells on Herr Professor Ausbach's microscope slides.

In this set of investigations he asks you to:
Study this first

  • Read and study about the properties of light, so you know what you are doing.

      Concentrate on:
    • light, history of light, and human vision
    • sources of light, color, speed, and interactions
    • refraction and reflection
    • prisms and bringing to a focus
    • lenses, magnification, objects and images
    • microscopes

    Then investigate
  • determine the refractive index for all the types of glass used in Brother Gregory's selection of lenses.

  • then determine the focal length and the amount of magnification provided by each lens.

  • make all this data into a table that lists the full set of properties for each lens in the box.
    Lens Data

Unknown Use your knowledge about the properties of the eyepiece and objective lenses to put together a microscope. Use this microscope to look at the cells on the slides sent by Herr Professor Ausbach.

  • open the box of Herr Professor Ausbach's prepared microscope slides, and read the notes he has provided about each specimen.

  • using this information, and your table which gives the properties of each lens, "build a microscope" that use two lenses (an eyepiece and an objective), and view each of the microscope slides.

  • compare what you see with known specimens in Bother Gregory's collection, and identify the unknown specimens sent by Herr Professor Ausbach.

Brother Gregory has given you all the tools you need to find the answers he wants. You are now his research assistant.

You must carry out the experiments, gather data, produce tables of properties for the lenses, use the lenses to examine the microscope slides, analyze your results and give Brother Gregory the names of the cells on the microscope slides.

(Hint: If you run into trouble, ask his mother for help!).

(bending light)

Investigation One

If you haven't already done so, read about what happens to light as it moves from air into glass (refraction).

The get Mendel's Mother to help you calculate the refractive index of the various types of glass used to make Brother Gregory's lenses.

Save this information in the form of a table. You will need it later.

(focal length and magnification)

Investigation Two
Read about the properties of lenses, and how light is bent in a special way as it passes through curved glass surfaces.

Every lens has a set of properties. One of these properties is the ability to bring light to a focus. You must know all about how lenses focus light and the property know as the focal length.

See how the image of an object can become magnified, as light from the object passes through a lens.

In this investigation you must use the "optical bench" to find the focal length and the magnification value all the lenses in Brother Gregory's box.

You must then add this information to your table of "Properties of Lenses". You will need all this information when you are putting together your own microscope.

(putting two lenses together)
Microscopes produce greatly magnified images of very small objects (such as cells) by passing the light from an object through two lenses.

A tiny object, such as a living cell on a microscope slide, is brought close to the focal point of a lens (the "objective" lens). A magnified image of that object is formed on the other side of this lens.

A second lens (the "eyepiece"), then magnifies this image again. A human observer (or a camera) can then view and capture this second image, which is now highly magnified.

The total magnification of the final image is obtained my multiplying together the individual magnifications of both the objective and eyepiece lenses.

Identifying Cells
Investigation Three
You must now try to identify the unknown cells on the microscope slides sent by Herr Professor Ausbach.

    Microscope Start

    Investigation Proceedure

  1. Choose one slide from the box.

  2. Choose an eyepiece lens for the top of the microscope.

    • Use the values you have found (and assembled into your table of "Properties of Lenses") to enter the correct value for the refractive index of this lens.

    • Similarly enter the value for the focal length of the lens.

    • Also the magnification value.

  3. Choose an objective lens for the bottom of the microscope.

    • As before, enter the values for refractive index, focal length and magnification, into the correct boxes.

  4. You should now be able to see an image (or a message).

  5. Use different lens combinations until you find an appropriate degree of total magnification, where the cells on the slide are clearly visible.

  6. Identify each of the types of cells on each of the slides provided by Herr Professor Ausbach, by comparing what you see with a library of cell images prepared by Brother Gregory.

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Science at a Distance
© 2000 Professor John Blamire