# What is the least number of microns

## Worksheet 1c: - How small / big are viruses?

Viruses: 15 to 400 nm (nanometers)

Bacteria: 0.3 to 1 µm (micrometers)

Human: 1.5 to 2 m (meters)

Small number prefixes: 10 Milli- (m) micro- (µ) nano- (n) pico- (p) femto- (f) |

400 nm = 0.4 µm

The largest viruses are as big as the smallest bacteria.

Most bacteria can be visualized with a light microscope. The resolution of the light microscope is not sufficient for viruses and very small bacteria. You need an electron microscope.

Resolving power of the human eye: ** 0.02 mm or 20 µm **

I.e. if two lines are 0.02 mm apart, then we can just recognize them as two lines; when they are closer together we see them as a line.

Look at a ruler or graph paper. The smallest division is millimeters, one millimeter is 1000 µm or 50 by 20 µm. So imagine if a millimeter were again divided into 50 graduation lines. Our eyes are so good that they could still tell two lines apart.

** Task: **

- Measure the item handed out so that you can easily see it with the eye. Imagine a virus that size, can you imagine how big you would be in relation to that?
- Since it's hard to estimate, try to figure it out.

Example of a ratio calculation: someone is 2 meters tall, his pencil is 10 cm long. If the pencil were 1 meter long, the person would be proportionally 20 meters tall. ** Note the different units (nm, cm, mm, m)! **

Use the back for your invoice and write down your result here:

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