Magnification is how many times larger the image is. Total magnification is eyepiece times objective.
Step 1: Something to Notice
Watch first. The explanation comes later.
A light microscope at 1000× and an electron microscope at 1000× produce completely different amounts of detail from the same specimen.
If the magnification is identical, what differs?
Step 2: Find Out
Isolate the variable that determines detail by holding magnification constant and changing the specimen size.
Step 1 — Predict
What sets the resolution limit of a light microscope?
Choose what you think will happen. You cannot see the experiment until you do — guessing first is what makes it worth watching.
Step 3: So Here Is Why
Now the explanation, after you have seen it happen.
Resolution
The smallest separation at which two points remain distinguishable. This is what limits detail.
Resolution The smallest distance at which two points can still be told apart.
Wavelength sets the limit
Light stops at about 200 nm. Electrons, with far shorter wavelength, reach about 0.1 nm.
Units of biological scale
Millimeter, micrometre, nanometre. A cell is tens of micrometres; a ribosome is tens of nanometres.
Every technique costs something
Electron microscopy needs a vacuum, so the specimen is dead and preparation can create artefacts.
Resolution, not magnification, is the limit
A light microscope cannot resolve detail finer than about half the wavelength of light, roughly 200 nanometres. Magnifying beyond that produces a larger blur, which is why electron microscopes exist.
Working in the right units
Cells are measured in micrometres, organelles and viruses in nanometres. Getting the order of magnitude right is more important than precision, and it is what makes a scale bar essential on any image.
Step 4: A Common Mistake
Lots of people think
“A more powerful microscope always shows more detail.”
Step 5: Reading a Scale Bar
The same idea somewhere new.
A published micrograph carries a scale bar rather than a magnification, because magnification changes whenever the image is resized and the bar does not. Measuring the bar and comparing it with a structure is how actual sizes are obtained from images, and it is the only method that survives reproduction.
Step 6: Think It Through
Practice makes it stick.
Actual Size
Problem 1 of 2
A structure is 30 mm on an image magnified 1500×. What is its actual size in µm?
µm
Same Magnification
Problem 2 of 2
Two microscopes both magnify 1000× and differ in detail. What differs?
Seeing and Measuring
1 of 5
What limits the resolution of a light microscope?
2 of 5
A 20 mm image structure at 500× magnification. Actual size in µm?
µm
3 of 5
Why do published micrographs carry a scale bar?
4 of 5
What is a cost of electron microscopy?
5 of 5
Roughly how large is a typical animal cell?
Step 7: Quick Check
Show what you know.
Question 1 of 1
Does more magnification always mean more detail?
Step 8: Explain It in Writing
Claim, evidence, then reasoning.
The question
Two microscopes both magnify 1000× and show very different detail. Explain, and state what limits each.
Fill in all three boxes. The reasoning box is the one that matters most.
What You Found Out
- Total magnification is eyepiece times objective.
- Resolution is the smallest separation still distinguishable, and it limits detail.
- Light microscopy stops near 200 nm because of the wavelength of light; electrons reach about 0.1 nm.
- Actual size is image size divided by magnification.