S4.1.2 For the adult
Microscopes and size
A cell is too small to see. How do scientists know how big it really is?
What this chapter teaches
A microscope makes an image bigger. Magnification is image size divided by real size, in the same unit. A micrometre is a thousandth of a millimetre and a nanometre a thousandth of a micrometre. An electron microscope has a better resolution than a light microscope.
Three questions to ask
There is no one right wording. Listen for the idea.
- A cell is 50 µm long and its drawing is 10 mm. What is the magnification?
- How many nanometres are in one micrometre, and why?
- Why will a light microscope never show a ribosome, however much it magnifies?
After the chapter, the learner can
- Calculate magnification from image size and real size
- Convert between millimetres, micrometres and nanometres
What they copy into their notebook
Magnification = image size ÷ real size, in the same unit. 1 mm = 1 000 µm. 1 µm = 1 000 nm. Light microscope: up to about ×1 500, cannot show ribosomes. Electron microscope: better resolution.