Calculate magnification and size of biological specimens using millimetres as units.

What is Magnification? 📷

Magnification tells us how many times bigger the image of a specimen looks compared to the real specimen. Think of it like zooming in on a photo: the closer you zoom, the bigger the picture appears.

Formula (inline LaTeX): $M = \dfrac{I}{O}$ where $I$ = image size and $O$ = object size.

Finding the Size of a Specimen 🧪

If you know the magnification and the size of the image, you can work out the real size:

Formula (inline LaTeX): $O = \dfrac{I}{M}$

Example: A microscope image of a cell is 5 mm long and the magnification is 100×. Real size = 5 mm ÷ 100 = 0.05 mm (50 µm).

Step‑by‑Step Example 🧩

1. Measure the image size with a ruler: 12 mm.
2. Read the magnification from the microscope: 200×.
3. Calculate real size: $O = 12\,\text{mm} ÷ 200 = 0.06\,\text{mm}$ (60 µm).

Tip: Always keep the units consistent (mm, µm, etc.).

Exam Tip Box 📚

Remember:

• Use the correct formula: $M = I/O$ or $O = I/M$.
• Check that you convert units if the answer is requested in micrometres (µm).
• Show all steps in your calculation; examiners look for clear reasoning.

Practice: If a specimen image is 3 mm and the magnification is 150×, what is the real size? (Answer: 0.02 mm or 20 µm).

Quick Reference Table 📊