Magnification
Magnification
- Cells are tiny, so we view them under a microscope.
- How many times bigger the image is = the magnification.
- A simple formula links image size, actual size and magnification.
The formula
$$\text{magnification} = \frac{\text{image size}}{\text{actual size}}$$
- image size = size in the drawing/photo; actual size = the real size.
- Magnification has no unit (e.g. ×250). Rearranged: $\text{actual size} = \dfrac{\text{image size}}{\text{magnification}}$.
Practice
Magnification is:
magnification = image size / actual size; it has no unit.
Practice
A structure has an image size of 5 mm at a magnification of ×250. What is its actual size in mm?
actual size = image ÷ magnification = 5 ÷ 250 = 0.02 mm.
Units
- Cells are often measured in micrometres (μm):
$$1\ \text{mm} = 1000\ \mu\text{m}, \qquad 1\ \mu\text{m} = 0.001\ \text{mm}$$
- Always put both sizes in the same unit before dividing. (e.g. image 5 mm at ×250 → actual = 5 ÷ 250 = 0.02 mm = 20 μm.)
Practice
How many micrometres are in 1 millimetre?
1 mm = 1000 μm (so 0.02 mm = 20 μm).
Practice
You must put the image size and actual size in the same unit before calculating magnification.
Both sizes must be in the same unit, or the magnification will be wrong.
You've got it
Key idea
- $\text{magnification} = \dfrac{\text{image size}}{\text{actual size}}$ (no unit)
- $\text{actual size} = \dfrac{\text{image size}}{\text{magnification}}$
- convert to the same unit first; $1\ \text{mm} = 1000\ \mu\text{m}$