Cell measurement

Greg Foot explains the main differences between light and electron microscopes

Light microscopes

Most animal cells range in size from 0.01 to 0.05 mm, and plant cells from 0.01 to 0.10 mm.

The human eye can see objects as small as around 0.05 mm. Therefore a microscope is needed to see cells in detail.

Microscopes magnify the image of a specimen - cells, tissues or other structures - so that it appears larger. The type of microscope most used in schools is 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.The components of a light microscope and their functions

Calculating the magnification of a compound microscope

A 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.

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?

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.

The formula to calculate magnification is:

\text{magnification} = \frac{\text{size of image}}{\text{real size of object}}

The formula shown in a magnification triangle:

A triangle showing how to calculate the magnification of an image