ELECTRON MICROSCOPES Flashcards
about electron microscopes
show a clearer and more detailed image than light microscopes
higher magnification
higher resolution
why do electron microscopes have a higher resolution
electron beam has a shorter wavelength than light
TEM
transmission electron microscope
beam of electrons passed through specimen
electrons pass through denser parts less easily so denser appears darker and so darker regions contain more structures
scattered electrons are captured on a photographic plate
2D
mag up to 250000x
res of 2nm
SEM
scanning electron microscope
specimen coated in a thin layer of metal
electromagnet focuses a beam of electrons
electrons bounced off the surface onto a photographic plate
3D
mag 100000x
res of 3-20nm
advantages of electron microscopes
higher resolution compared to light so smaller organelles can be seen
SEM produces 3D images
limitations of electron microscopes
specimens must be in a vacuum so cannot see living specimens
images in black and white
complex staining process so image may contain artefacts
TEM specimens must be very thin to allow electrons to penitrate
TEM produces flat 2D images but can be overcome by taking a series of sections
SEM has a lower resolving power than TEM but still better than alight micriscope
what are artefacts
images you can see down the microscope that arent part of the specimen
e.g. dust, air bubbles, fingerprints
usually during the preparation of the specimen
