A world below the eye
Show on a big screenLook at this full stop. Many living things are far smaller. Living things too small to see one by one are called microbes.
Sizes are in mm, short for millimetre.
- A microbe is about 0.005 mm across.
- An eye can see about 0.1 mm or more. The microbe is far too small.
- A lens of power ×100 makes it look 100 times bigger.
- It now looks 0.5 mm. That is more than 0.1 mm, so you can see it.
The rule
A microorganism, or microbe, is a tiny living thing. An eye alone cannot see it. A lens is curved glass. A lens has a power, such as ×100. Size seen is how big the thing looks.
A microscope lens makes a thing look bigger. Size seen = real size × power. An eye can see about 0.1 mm or more. Anything smaller needs a lens.
| Thing | Size |
|---|---|
| A grain of rice | 6 mm |
| The eye's limit | 0.1 mm |
| A microbe | 0.005 mm |
Robert Hooke used a microscope around 1665. He looked at cork, which is light tree bark. He named the tiny boxes in cork cells. Antonie van Leeuwenhoek used lenses to see bacteria.
Increase the power. Find the power where you first see the microbe.
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Try the lab to finish this lesson.