Electron Microscopy Investigation
The electron microscope was first made when biologists found a problem
with the resolution of a light microscope. Resolution means “the
ability to distinguish between two points”; the problem is that the
maximum resolution of a light microscope is 200nm. So if two points
are closer together than 200nm they are seen as one. One example of
this problem is that under a light microscope the centrioles in an
animal cell appear as one, however when viewed under an electron
microscope we can see that there are two centrioles at right angles to
each other. Magnifying the image or using a higher magnification
cannot overcome this problem, as we increase the magnification we do
not get a better resolution just an enlarged image. In fact if we
increase the magnification beyond a point it only decreases the
resolution.
The light a light microscope uses is between 400nm wavelength to 700nm
wavelength as this is the visible light spectrum. 400nm being the
smallest wavelength of visible light (violet light). Cells like
ribosomes are far to small to interfere with light waves, ribosomes
are about 22nm in diameter. The limit of resolution is half the
wavelength of the radiation used, in this case 400nm (violet light),
to view the specimen with. So anything below 200nm cannot be seen
clearly, if at all. Another flaw of the light microscope that that if
an object is transparent it will allow light to pass through it
therefore cannot be seen using a light microscope. This is why samples
are dyed with chemicals like iodine before they can be viewed.
One solution is to use a radiation with a shorter wavelength than the
smallest visible light. Ultra violet and x-ray microscopes have been
built but faced many problems; one problem is that x-rays are very
hard to focus. A better solution was to use electrons, an electron is
a negatively charged particle witch orbits an atoms nucleus. When a
metal becomes very hot, meaning it has an increase in energy, its
electrons also gain energy some gain so much energy they break free of