Magnification
| English | Chinese | Pinyin |
|---|---|---|
| microscope | 显微镜 | xiǎn wēi jìng |
| magnification | 放大倍数 | fàng dà bèi shù |
| micrometres | 微米 | wēi mǐ |
| scale bar | 比例尺 | bǐ lì chǐ |
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:
Magnification = image ÷ actual.
An image is 40 mm across and the real object is 0.5 mm. What is the magnification?
40 ÷ 0.5 = ×80.
Magnification is a ratio and so has no units.
It compares two lengths, so the units cancel.
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)?
Actual = 60 ÷ 300 = 0.2 mm.
How many micrometres (µm) are in 1 millimetre (mm)?
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)