use an eyepiece graticule and stage micrometer scale to make measurements and use the appropriate units, millimetre (mm), micrometre (µm) and nanometre (nm)

Sourav PanOctober 28, 2024

Answered

Objective: To accurately measure specimens using an eyepiece graticule and a stage micrometer scale, and to express measurements in the appropriate units (mm, µm, nm).

Equipment and Tools:

1. Light Microscope with:
   • Eyepiece Graticule: A reticle with a measured scale in one of the eyepieces.
   • Stage Micrometer Scale: A slide with precise measurements, used for calibration.
2. Specimen Slide

Step-by-Step Procedure:

Calibration of Eyepiece Graticule

1. Place the Stage Micrometer Scale on the microscope stage.
2. Focus on the stage micrometer scale using the objective lens (typically the 4X or 10X objective for initial focusing).
3. Switch to the Eyepiece with the Graticule and ensure the graticule’s scale is sharp and clear.
4. Superimpose the graticule scale over the stage micrometer scale by adjusting the stage (not the focus).
5. Identify a clear starting point (e.g., the edge of a line) on both the graticule and the stage micrometer.
6. Count the number of graticule units that correspond to a known length on the stage micrometer (e.g., 1 mm = 1000 µm).
7. Record the calibration:
   • Example Calibration: 1 mm on stage micrometer = 50 units on eyepiece graticule
   • Conversion Factor: 1 graticule unit = 20 µm (since 1000 µm / 50 units = 20 µm/unit)

Measuring a Specimen

1. Replace the Stage Micrometer with your Specimen Slide and focus on the specimen.
2. Ensure the Eyepiece Graticule is still in place and clear.
3. Position the specimen so that a feature of interest aligns with the graticule scale.
4. Measure the feature by counting the graticule units:
   • Example Measurement: A cell diameter spans 30 graticule units.
5. Convert the measurement to the appropriate unit using the calibration factor:
   • Actual Measurement: 30 graticule units × 20 µm/unit = 600 µm

Choosing the Appropriate Unit (mm, µm, nm)

• Millimeters (mm): Suitable for larger measurements, typically not used for microscopic specimens due to their small size.
• Micrometers (µm): Ideal for most microscopic measurements, as specimens often fall within this size range (e.g., cells, small organisms).
• Nanometers (nm): Used for extremely small measurements, usually beyond the resolution of light microscopes (e.g., molecular structures, some virus sizes). Note: For measurements in nm, electron microscopes (TEM, SEM) are typically required.

Example Measurements with Unit Selection

Remember: Always calibrate your eyepiece graticule with a stage micrometer for each objective lens used, as the magnification (and hence the calibration factor) changes with different lenses.