Using microscopes

The microscopes required practical is the most commonly under-revised topic as it seems easy. It is also a common area of lost marks!

Make sure you revise the names of the key parts:

• Eye piece lens (at top) - this usually magnifies the image by x10 or x5.
• Objective lens (small ones in the middle). There are usually 3-4 of these and they are different powers, ranging from x4, x10, x40 (and sometimes x100).
• Multiply the power of both lenses to get the total magnification, e.g. 4 x 5 = x20
• Coarse focus - the dial at the side is twisted to focus the image
• Do not use the phrase "zoom in" but state the image is magnified.
• The magnification be calculated using the phrase I AM - or Image = Actual size x magnification

Magnification = Image / Actual size

Try using the formula triangle (see below)

Magnification is the number of times bigger an image is compared to the actual size

Resolution is the ability to distinguish between two different points.

Light microscopes are limited by their resolution rather than magnification

Scanning electron microscope

The alternative is called the transmission electron microscope and this produces images showing sections through very small objects, e.g it can see ribosomes.