Understanding Micrometry: An In-Depth Exploration

Micrometry and Measurement of Cell Size

Micrometry is the technique used to measure microscopic objects like cells, bacteria, or tissue structures using a light microscope. Since these objects are too small to measure with the naked eye, we use two primary tools: the stage micrometer and the ocular micrometer.

Tools:

  1. Stage Micrometer – a glass slide with a precise engraved scale, used as a ruler for calibration.
  2. Ocular Micrometer – a scale in the eyepiece, used to measure specimens once calibrated.

Stage micrometer = ruler, Ocular micrometer = measuring tool under microscope

Step 1: Calibrating the Ocular Micrometer

The ocular micrometer scale does not show real size by itself, so it must be calibrated using a stage micrometer.

Formula:
Ocular Value (OV in μm) = Stage Micrometer Division (μm) ÷ Number of Ocular Divisions

OV gives the actual size of each ocular division.

Step 2: Using 4× Objective Lens

  1. Place the stage micrometer on the microscope stage and focus with 4× objective.
  2. Align the ocular scale with the stage micrometer scale.
  3. Count how many ocular divisions correspond to a stage division.

Example:

  • 1 stage division = 100 μm
  • 10 ocular divisions = 1 stage division
  • 1 ocular division = 100 ÷ 10 = 10 μm

If a cell spans 8 ocular divisions:

  • Cell size = 8 × 10 = 80 μm

Step 3: Using 10× Objective Lens

  1. Switch to 10× objective and focus.
  2. Align scales and count ocular divisions per stage division.

Example:

  • 1 stage division = 40 μm
  • 10 ocular divisions = 1 stage division
  • 1 ocular division = 40 ÷ 10 = 4 μm

If a cell spans 12 ocular divisions:

  • Cell size = 12 × 4 = 48 μm

Step 4: Using 12.5× Objective Lens

  1. Focus with 12.5× objective.
  2. Align ocular and stage scales carefully.
  3. Count ocular divisions per stage division.

Example:

  • 1 stage division = 32 μm
  • 10 ocular divisions = 1 stage division
  • 1 ocular division = 32 ÷ 10 = 3.2 μm

If a cell spans 15 ocular divisions:

  • Cell size = 15 × 3.2 = 48 μm

Step 5: Using 40× Objective Lens

  1. Focus with 40× objective (high power).
  2. Align scales carefully.

Example:

  • 1 stage division = 10 μm
  • 10 ocular divisions = 1 stage division
  • 1 ocular division = 10 ÷ 10 = 1 μm

If a cell spans 18 ocular divisions:

  • Cell size = 18 × 1 = 18 μm

Step 6: Using 100× Objective Lens (Oil Immersion)

  1. Use oil immersion and focus with 100× objective.
  2. Align scales carefully.

Example:

  • 1 stage division = 4 μm
  • 10 ocular divisions = 1 stage division
  • 1 ocular division = 4 ÷ 10 = 0.4 μm

If a cell spans 25 ocular divisions:

  • Cell size = 25 × 0.4 = 10 μm

Calibration must be repeated for each objective lens.

Step 7: Measuring Specimen

  1. Place the specimen on the stage.
  2. Focus using the same objective lens used for calibration.
  3. Align the start of the cell with the zero of the ocular scale.
  4. Count the ocular divisions the cell spans.
  5. Multiply by ocular value (OV) to get the actual size.
  6. Repeat measurements for accuracy.

Step 8: Teacher Tips

  • Always recalibrate for each objective lens.
  • Use fine focus to avoid parallax errors.
  • For oil immersion, use only immersion oil.
  • Practice increases accuracy and speed.

Conclusion

Micrometry allows accurate measurement of microscopic objects:

  • Stage micrometer → calibration
  • Ocular micrometer → measurement
  • Formula: Cell size = Number of ocular divisions × Ocular value (μm)

With practice, students can confidently measure any microscopic specimen.

Micrometry aur Cell Size Measurement (Roman Urdu)

Micrometry ka matlab hai microscopic objects jaise cells ya bacteria ka size measure karna microscope ki madad se. Ye objects naked eye se nahi dikhte, is liye hum do tools use karte hain:

  1. Stage Micrometer – ek glass slide pe engraved scale hota hai, jo calibration ke liye use hota hai (ruler).

  2. Ocular Micrometer – eyepiece me scale, jo calibrated hone ke baad specimen measure karta hai.

Stage micrometer = ruler, Ocular micrometer = microscope ka measuring tool

Step 1: Ocular Micrometer Calibrate Karna

Ocular scale apne aap accurate size nahi batata, isliye hamesha stage micrometer se calibrate karna padta hai.

Formula:
Ocular Value (OV in μm) = Stage Micrometer Division (μm) ÷ Number of Ocular Divisions

Ye OV batata hai ke 1 ocular division ka real size kitna hai.

Step 2: 4× Objective Lens Use Karna

  1. Stage micrometer ko microscope stage pe rakho aur 4× lens se focus karo.
  2. Ocular scale ko stage scale ke saath align karo.
  3. Count karo ocular divisions per stage division.

Example:

  • 1 stage division = 100 μm
  • 10 ocular divisions = 1 stage division
  • 1 ocular division = 100 ÷ 10 = 10 μm

Agar cell 8 ocular divisions span kare:

  • Cell size = 8 × 10 = 80 μm

Step 3: 10× Objective Lens Use Karna

  1. 10× lens pe focus karo.
  2. Align scales aur count karo ocular divisions per stage division.

Example:

  • 1 stage division = 40 μm
  • 10 ocular divisions = 1 stage division
  • 1 ocular division = 40 ÷ 10 = 4 μm

Cell spans 12 ocular divisions →

  • Cell size = 12 × 4 = 48 μm

Step 4: 12.5× Objective Lens Use Karna

  1. 12.5× lens pe focus karo.
  2. Align ocular aur stage scales carefully.
  3. Count ocular divisions per stage division.

Example:

  • 1 stage division = 32 μm
  • 10 ocular divisions = 1 stage division
  • 1 ocular division = 32 ÷ 10 = 3.2 μm

Cell spans 15 ocular divisions →

  • Cell size = 15 × 3.2 = 48 μm

Step 5: 40× Objective Lens Use Karna

  1. 40× lens pe focus karo.

  2. Align scales carefully.

Example:

  • 1 stage division = 10 μm
  • 10 ocular divisions = 1 stage division
  • 1 ocular division = 10 ÷ 10 = 1 μm

Cell spans 18 ocular divisions →

  • Cell size = 18 × 1 = 18 μm

Step 6: 100× Objective Lens (Oil Immersion) Use Karna

  1. Oil immersion lens me oil lagao aur 100× pe focus karo.

  2. Align scales carefully.

Example:

  • 1 stage division = 4 μm
  • 10 ocular divisions = 1 stage division
  • 1 ocular division = 4 ÷ 10 = 0.4 μm

Cell spans 25 ocular divisions →

  • Cell size = 25 × 0.4 = 10 μm

Har objective lens ke liye alagh calibration zaruri hai.

Step 7: Specimen Measure Karna

  1. Slide place karo.

  2. Focus karo same objective lens pe jo calibration me use hua.

  3. Cell ke start ko ocular scale ke zero pe align karo.

  4. Count karo ocular divisions jo cell span kar raha hai.

  5. Multiply karo ocular value se → real size milta hai.

  6. Multiple readings lo accuracy ke liye.

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