Most cells are far too small to see. A light microscope makes them look bigger with two lenses: the eyepiece you look into and an objective lens just above the slide. You will need multiplication to find how strong it is.
Key idea
Total magnification = eyepiece power × objective power. A 10× eyepiece with a 40× objective gives $10 \times 40 = 400$×. Higher power shows a smaller area of the slide, looking larger.
Why it works
The objective makes an image 40 times wider than the cell. The eyepiece then magnifies that image 10 times more. Each lens multiplies what the one before it made, so the powers multiply, they do not add. The circle you look through stays the same size, so when everything looks 4 times wider, only a quarter as much of the slide fits across.
Worked examples
Worked example: Total magnification
A microscope has a 10× eyepiece and a 100× objective. What is the total magnification?
- Multiply: $10 \times 100 = 1000$.
Answer: 1,000×
Worked example: Working backward
You see a cell at 400× with a 10× eyepiece. Which objective are you using?
- Total = eyepiece × objective.
- Objective = $400 \div 10 = 40$.
Answer: The 40× objective.
- Start with the lowest-power objective and focus with the coarse knob.
- Center what you want to see, then turn to a higher power.
- At high power, focus only with the fine knob.
- Use the diaphragm to adjust the light; high power often needs more.
Common mistake
Adding the powers: 10× and 40× is not 50×. Check with a story: if one lens makes it 4 times bigger and the next makes that 10 times bigger, it is now 40 times bigger, not 14. Another slip is expecting to see more of the slide at high power; you see less of it, larger.