Cell measurement
Greg Foot explains the main differences between light and electron microscopes
Light microscopes
Most animal cells range in size from 10 - 50 μm, and plant cells from 10 - 100 μm.
The human eye can see objects as small as 50 μm. We require a microscope to see cells in further detail.
Microscopes magnify the image of a specimen - a cell, tissue, etc. - so that it appears larger. The type of microscope you use in a school laboratory is as a A microscope in which the lens is close to the sample being magnified..
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 therefore be varied according to the size of the specimen to be viewed 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.
It is 10 × 40 = 400.
Calculating the magnification of an image
Microscopes use lenses to magnify the image of a biological specimen so that it appears larger. Photographs can be taken through a microscope. Sometimes you may be asked to make measurements from a photograph in order to calculate the actual size of an organelle or its magnification.
The formula to calculate magnification is:
\( \text{magnification} = \frac{size~of~image}{real~size~of~object}\)