Using a microscope: magnification
Look at onion skin cells and cheek cells through a school microscope. Turn to stronger lenses and find out how magnification changes what you see.
Core concept
A microscope's magnification is the eyepiece's magnification times the objective's; the more it magnifies, the bigger and fewer the cells we see
Topic: Cells
cell: The tiny building block that every living thing is made of. All key words are far too small to see with our eyes alone: an onion skin cell is about a quarter of a millimetre long and a cheek cell even smaller. A compound microscope uses two lenses to magnify them. The eyepiece, which you look into, usually magnifies 10 times (10×). The objective, just above the slide, can be turned to 4×, 10× or 40×. The total magnification is the two multiplied together: a 10× eyepiece with a 40× objective magnifies 400 times. The stronger the lenses, the bigger each cell looks, but the smaller the part of the slide you can see at once.
What you will learn
- Name the eyepiece and objective lenses of a microscope.
- Work out the total magnification: eyepiece × objective.
- Explain why stronger magnification shows fewer, bigger cells.
- Compare onion skin cells (plant) with cheek cells (animal).
Before you start
- Know that living things are made of cells.
Materials
- An onion, iodine solution, a clean ice-cream stick for cheek cells, methylene blue
Equipment
- A school microscope, slides and cover slips
Procedure
- Look at onion skin with the 10× eyepiece and the 4× objective, and record.
- Turn to the 10× objective, then the 40×, recording each.
- Change the slide to cheek cells at 400× and record.
- Swap to the 15× eyepiece with the 40× objective and record.
How this simulation is simplified
- An onion skin cell is 0.25 mm long and a cheek cell 0.06 mm across.
- The circle you see is 18 mm wide through a 10× eyepiece and 12 mm through a 15×, divided by the objective's magnification.