Magnification
Introduced| English | Meaning |
|---|---|
| microscope/ˈmaɪkrəskəʊp/ | An instrument used to magnify objects too small to see clearly with the unaided eye. |
| magnification/ˌmæɡnɪfɪˈkeɪʃn/ | The ratio of an image's size to the corresponding actual size of the object. |
| micrometres/ˈmaɪkrəʊmiːtəz/ | Units of length each equal to one millionth of a metre. |
| scale bar/skeɪl bɑː/ | scale bar |
Seeing the invisible
- Cells are far too small to see with the naked eye — we need a microscope 显微镜.
- And to describe what we see, we need to work out the magnification 放大倍数.
Magnification lab
magnification = image size / actual size
Change actual size and see how image size links to magnification.
Magnification is calculated as:
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Magnification = image ÷ actual.
An image is 40 mm across and the real object is 0.5 mm. What is the magnification?
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40 ÷ 0.5 = ×80.
Magnification is measured in millimetres.
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False. Magnification is image size ÷ actual size, a ratio of two lengths, so the units cancel and it has no units.
The magnification formula
- Magnification = image size ÷ actual size.
- Rearranged: actual size = image size ÷ magnification.
Worked example. A cell's image is 30 mm across. The real cell is 0.06 mm. Magnification = 30 ÷ 0.06 = ×500.
Cover the quantity you want in the triangle to get its formula
An image is 60 mm and the magnification is ×300. What is the actual size (mm)?
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Actual = 60 ÷ 300 = 0.2 mm.
How many micrometres (µm) are in 1 millimetre (mm)?
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1 mm = 1000 µm.
Units and conversions
- Cells are measured in micrometres 微米 (µm): 1 mm = 1000 µm.
- Always convert both sizes to the same unit before dividing.
Scale bars 比例尺
- A scale bar on an image shows how big a real length is.
- Measure the bar, compare to the value it represents, and you can find the magnification or real sizes.
Keep the units the same. A common mistake is dividing millimetres by micrometres. Convert both to the same unit first, or your magnification will be 1000 times wrong.
You've got it
- magnification = image size ÷ actual size (no units — it's a ratio)
- rearrange to find actual size = image ÷ magnification
- convert both sizes to the same unit first (1 mm = 1000 µm)
Write from an actual size of 50 micrometres
- A drawing of a cell is 20 mm across.
- The magnification is 400.
What is the actual width of the cell in micrometres?
Actual size is image size divided by magnification.
The image is 20 mm at a magnification of 400. What is the actual width?
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20 divided by 400 is 0.05 mm, or 50 micrometres.