Light microscopes

Greg Foot explains the main differences between light and electron microscopes

Cells range in size:

  • most animal cells are between 0.01 mm – 0.05 mm
  • most 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 biological specimen so that it appears larger. The type of microscope used in a school laboratory 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.Compound microscope

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 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.

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.

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:

\textup{magnification} = \frac{\textup{size~of~image}}{\textup{real~size~of~object}}

A triangle showing how to calculate the magnification of an imageThe formula shown in a magnification triangle