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 compound microscope.

Microscopes magnify the image of a specimen – cells, tissues of other structures – so that it appears larger. The type of microscope you have used in the school laboratory is a compound microscope.Most school microscopes now have built in light source, but some may have a mirror to reflect light instead

Calculating the magnification of the microscope

The compound microscope uses two lenses to magnify the specimen – the eyepiece and an objective lens.

In most microscopes, there is a choice of objective lenses to use. Magnification 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.

curriculum-key-fact
Magnification of the microscope = magnification of eyepiece × magnification of objective.

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}