Measuring Techniques D3

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Measuring TechniquesD3

• Part III
• Measuring the Size of a Specimen Using a Stage
  Micrometer and an Ocular Micrometer

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Preface

• Before beginning this module, you should be
  familiar with the parts, use, and care of the
  compound microscope.
• If you are unsure about the microscopes
  operation, please review the Use of the
  Microscope module.
• Mishandling of the microscope can lead to damage
  of the instrument.

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Module Requirements

• To complete this module, the following equipment
  will be provided to you by an SLC assistant.
• -microscope with ocular micrometer
• -prepared microscope slide
• -stage micrometer
• -worksheet
• If materials are missing or you are having
  problems getting started, please ask one of the
  SLC staff for help.

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Notes

• The Stage and Ocular Micrometer Technique is the
  most precise method used for measuring
  microscopic specimens here at the Science
  Learning Center.
• An ocular micrometer consists of an ocular lens
  with equal space gradations that, unlike the
  stage micrometer, have no units.
• Look into the microscope at your workstation to
  make sure you see the ocular micrometer. If you
  dont see the micrometer, contact a Student
  Assistant.

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Notes

• If you have completed module D1, you should be
  familiar with the stage micrometer. The modules
  here at the Science Learning Center use a 2mm
  micrometer. In lab situations though, always
  check the label for the calibration.

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• Position the stage micrometer on the
  microscopes stage and clearly focus the scale
  using the 10X objective lens.
• Note If you are having trouble finding the scale
  at 10X, switch to a lower power, such as 4X, to
  center scale. Then select the 10X objective and
  use the fine adjustment to focus.

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Notes

• Though stage micrometers are very accurate, we
  cannot place both a specimen on a slide and the
  micrometer under the microscope at the same time.
• To solve this dilemma, we can make use of the
  ocular scale. Its important to remember that
  the ocular micrometer divisions have no units,
  and that each division will change with each
  magnification. Therefore, you must calibrate the
  ocular scale before you can use it.

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Notes

• To calibrate the ocular scale, use the stage
  micrometer. Your calibration will determine how
  many millimeters are represented by one division
  on the ocular scale, or one ocular division.
• If you find that one ocular division equals
  0.3mm, then you know two divisions equal 0.6mm
  and so forth.
• Therefore, if you find a specimen covers three
  ocular divisions, you will know that it measures
  0.9mm in length.

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Calibration

• With the stage micrometer in focus, rotate the
  eyepiece until the ocular micrometer aligns with
  the stage micrometer.

This example shows that one ocular division (od)
equals 0.1mm.
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Example

• Using the ocular division from our last slide,
  we can measure the size of this animal. Based on
  what you have learned, can you figure out its
  length?

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Example

• This animal occupies 3.4 ocular divisions.
  We found that 1 od is equal to 0.1 mm. So the
  size of this animal is 0.34mm.
• The simple equation can be written as
• ( of ocular divisions) x ( of mm per division)
  
• diameter of cell in mm

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Notes

• The last slide gave a quick example. Do not
  take for granted that all ocular micrometers are
  calibrated the same. Always calibrate your
  instrument before making your measurements.

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Example

• Suppose your microscope had an ocular lens
  where one division equaled 0.02mm. You found
  that your specimen covers 3 ocular divisions.
  What is the length of your specimen?
• (3) x (0.02mm) 0.06mm

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Try it!

• Follow the procedure with the practice slides
  provided. Remember its good practice to
  calibrate your microscope for each specimen.

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Module Completed!

• Please return to the main desk to obtain a post
  test from your friendly Science Learning Center
  personnel.