A2.2 Magnification Calculations and Microscopy Skills

Learning Goals and Microscopy Skills

• Calculate magnification ($M$), actual size ($A$), and image size ($I$) of a micrograph.

• Convert between units: centimetre ($cm$), millimetre ($mm$), micrometre ($μ m$), and nanometre ($nm$).

• Estimate specimen size in micrographs and create biological drawings.

Biological Drawing Guidelines (Marking Codes)

• T1: Label name, specimen, date, magnification.

• T2: Use smooth, continuous lines.

• T3: Use stippling instead of shading.

• T4: Ensure accurate drawing representation.

• T5: Label all visible structures properly.

Magnification Formulas

• $Magnification = \frac{\text{Image Size}}{\text{Actual Size}}$

• $Actual\,Size = \frac{\text{Image\,Size}}{Magnification}$

• $Image\,Size = Actual\,Size \times Magnification$

• Tip: Image size is always determined using a ruler.

• Tip: Ensure units for Image size and Actual size are identical before calculating.

Unit Conversion Standards

• $1\,cm = 10\,mm$

• $1\,mm = 1000\,μ m$

• $1\,μ m = 1000\,nm$

• To convert from $mm \rightarrow μ m \rightarrow nm$, multiply by $1000$ for each step.

• To convert from $nm \rightarrow μ m \rightarrow mm$, divide by $1000$ for each step.

Scale Bars and Micrographs

• A micrograph is a photo taken through a microscope that can be further magnified.

• Scale bars are straight lines representing the actual size of the specimen.

• $Magnification = \frac{\text{Measured Length of Scale Bar (with ruler)}}{\text{Actual Size indicated on Scale Bar}}$

• Example: A $10\,mm$ long scale bar labeled as $1\,μ m$ equals a magnification of $10,000 \times$.

Practice Calculations and Examples

• Conversion practice:

  • $5\,mm = 5000\,μ m$

  • $10\,μ m = 10,000\,nm$

  • $1500\,nm = 1.5\,μ m$

  • $21\,mm = 21,000,000\,nm$

  • $32,000,000\,nm = 32\,mm$

• Problem 4: An onion cell image is magnified $140 \times$ and measures $52,000\,μ m$.

  • $Actual\,Size = \frac{52,000\,μ m}{140} = 371.4\,μ m$ (approximately).

• Proper Nouns for Study: Volvox, Amoeba, Paramecium, and Helicobacter pylori.