Measuring TechniquesD3

Part III: Part III:

Measuring the Size of a Specimen Measuring the Size of a Specimen Using a Stage Micrometer and an Using a Stage Micrometer and an

Ocular Micrometer Ocular Micrometer

Preface: Before beginning this module, you should Before beginning this module, you should

be familiar with the parts, use, and care of be familiar with the parts, use, and care of the compound microscope.the compound microscope.

If you are unsure about the microscope’s If you are unsure about the microscope’s operation, please review the operation, please review the Use of the Microscope module. module.

Mishandling of the microscope can lead to Mishandling of the microscope can lead to damage of the instrument.damage of the instrument.

Module Requirements: To complete this module, the following equipment will be To complete this module, the following equipment will be

provided to you by an SLC assistant.provided to you by an SLC assistant.

-microscope with ocular micrometer-microscope with ocular micrometer

-prepared microscope slide -prepared microscope slide

-stage micrometer-stage micrometer

-worksheet-worksheet

If materials are missing or you are having problems getting If materials are missing or you are having problems getting started, please ask one of the SLC staff for help.started, please ask one of the SLC staff for help.

NotesThe Stage and Ocular Micrometer Technique is The Stage and Ocular Micrometer Technique is the most precise method used for measuring the most precise method used for measuring microscopic specimens here at the Science microscopic specimens here at the Science Learning Center.Learning Center.An ocular micrometer consists of an ocular lens An ocular micrometer consists of an ocular lens with equal space gradations that, unlike the stage with equal space gradations that, unlike the stage micrometer, have no units.micrometer, have no units.Look into the microscope at your workstation to Look into the microscope at your workstation to make sure you see the ocular micrometer. If you make sure you see the ocular micrometer. If you don’t see the micrometer, contact a Student don’t see the micrometer, contact a Student Assistant.Assistant.

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

Position the stage micrometer on the microscope’s stage and Position the stage micrometer on the microscope’s stage and clearly focus the scale using the 10X objective lens.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 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.center scale. Then select the 10X objective and use the fine adjustment to focus.

Notes Though stage micrometers are very accurate, we Though stage micrometers are very accurate, we

cannot place both a specimen on a slide and the cannot place both a specimen on a slide and the micrometer under the microscope at the same micrometer under the microscope at the same time.time.

To solve this dilemma, we can make use of the To solve this dilemma, we can make use of the ocular scale. It’s important to remember that the ocular scale. It’s important to remember that the ocular micrometer divisions have no units, and ocular micrometer divisions have no units, and that each division will change with each that each division will change with each magnification. Therefore, you must calibrate the magnification. Therefore, you must calibrate the ocular scale before you can use it. ocular scale before you can use it.

NotesTo calibrate the ocular scale, use the stage To calibrate the ocular scale, use the stage micrometer. Your calibration will determine how micrometer. Your calibration will determine how many millimeters are represented by one division many millimeters are represented by one division on the ocular scale, or one ocular division.on the ocular scale, or one ocular division.

If you find that one ocular division equals 0.3mm, If you find that one ocular division equals 0.3mm, then you know two divisions equal 0.6mm and so then you know two divisions equal 0.6mm and so forth. forth.

Therefore, if you find a specimen covers three Therefore, if you find a specimen covers three ocular divisions, you will know that it measures ocular divisions, you will know that it measures 0.9mm in length. 0.9mm in length.

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

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

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

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

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

Example

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

(3) x (0.02mm) = 0.06mm(3) x (0.02mm) = 0.06mm

Try it!Follow the procedure with the practice Follow the procedure with the practice slides provided. Remember it’s good slides provided. Remember it’s good practice to calibrate your microscope for practice to calibrate your microscope for each specimen.each specimen.

Module Completed!

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