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metre mm = 1 m
millimetre mm = 10-3 m
micrometre µm = 10-6 m
nanometre nm = 10-9 m
Magnification and Resolution
If a microscope uses more lenses, it can magnify by a higher amount , but this doesn't nesscarily
mean more detail is observed. This instead depends on the resolving power of the microscope, the
smallest distance two separate objects can be distinguished.
The resolving power is limited by the wavelength of light, to improve resolving power, a shorter
light wavelength is needed, this can be solved with a blue filter, as blue has the shortest light
Magnification = how much bigger a sample is observed under the microscope then its actual size.
Resolution= Shortest distance two separate objects can be distinguished.
The resolution of an image is limited by the wavelength of radiation used to view the sample. This
is because when objects in the specimen are much smaller than the wavelength of the radiation
being used, they do not interrupt the waves, and so are not detected.
The wavelength of light is much larger than the wavelength of electrons, so the resolution of the
light microscope is a lot lower.
Light Microscope Electron Microscope
Cheap to purchase (£100 500) Expensive to buy (over £ 1 000 000).
Cheap to operate. Expensive to produce electron beam.
Small and portable. Large and requires special rooms.
Simple and easy sample preparation. Lengthy and complex sample prep.
Material rarely distorted by preparation. Preparation distorts material.
Vacuum is not required. Vacuum is required.
Natural colour of sample maintained. All images in black and white.
Magnifies objects only up to 2000 times Magnifies over 500 000 times.
Specimens are dead, as they must be fixed in
Specimens can be living or dead
plastic and viewed in a vacuum
The electron beam can damage specimens and
they must be stained with an electron-dense
Stains are often needed to make the cells visible
chemical (usually heavy metals like osmium,
lead or gold).
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A beam of electrons is passed over the surface of the specimen, these are reflected off the specimen
as it has been coated in heavy metals, these are then focused on a fluorescent screen in order to
make up the image. This is good for thicker specimens, as electrons don't have to pass through
sample to form image, so this enables 3D effect, despite this, the resolution is lower than a standard
transmission electron microscope.…read more