Cell structure

Light microscopes

Greg Foot explains the main differences between light and electron microscopes

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

The human eye can see objects as small as around 0.05 mm. We therefore need a microscope to see cells in any detail.

Microscopes magnify the image of a specimen - cells, tissues of other structures - so that it appears larger. The type of microscope used in the school laboratory is a compound microscope. Compound microscopes can have a built-in light source or a mirror which reflects light from a light source to illuminate the specimen.

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.

Calculating the magnification of the microscope

The compound microscope uses two lenses to magnify the specimen - the eyepiece lens 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.

The total magnification can be calculated by multiplying the magnifying powers of the two lenses together.

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

So, if the magnification of an eyepiece lens is ×10 and the objective lens is ×4, the total magnification of the microscope is:

magnification of eyepiece lens × magnification of objective lens = 10 × 4 = ×40.

Question

If the magnification of an eyepiece lens is ×10 and the objective lens is ×40, what is the total magnification of the microscope?

×400.

It is 10 ×40 = ×400.