Cell measurement
Greg Foot explains the main differences between light and electron microscopes
Light microscopes
Cells range in size:
- animal cells are between 0.01 mm – 0.05 mm
- plant cells are between 0.01 mm – 0.10 mm
The human eye can see objects as small as around 0.05 mm. A microscope is required to see cells in any detail.
Microscopes magnify the image of a In microscopy, a whole organism, cells, tissues, a small piece of tissue, or other structures, eg hair, pollen grains, that are viewed with a microscope. so that it appears larger. The type of microscope used in a school laboratory is a A compound microscope uses two lenses, the objective lens and the eyepiece. The very short focal length objective lens produces a greatly-magnified image, then the short focal length eyepiece magnifies this further. .
Calculating the magnification of the microscope
The compound microscope uses two lenses to magnify the specimen – the The eyepiece, or ocular, is the lens at the top of a compound microscope. It has a longer focal length than the objective lens and magnifies the image produced by the objective. and an In a compound microscope, the lens closest to the specimen has a very short focal length and produces a greatly magnified image of the specimen. .
In most microscopes, there is a choice of objective lenses to use. The amount that an image of something is scaled up when viewed through a microscope. can be varied according to the size of the specimen and the level of detail required.
The magnification of a lens is shown by a multiplication sign followed by the amount the lens magnifies, eg ×10.
So, if the magnification of an eyepiece is ×10 and the objective is ×4, the magnification of the microscope is:
magnification of eyepiece × magnification of objective
= 10 × 4
= 40
Question
If the magnification of an eyepiece is ×10 and the objective is ×40, what is the magnification of the microscope?
×400.
Calculating the magnification of an image
Microscopes use lenses to magnify the image of a biological specimen so that it appears larger.
The formula to calculate magnification is:
\(magnification=\frac{size\; of\; image}{real\; size\; of\; object}\)