Microscopes Flashcards
What is the resolution?
How sharp an image is and how easy it is to distinguish between 2 points on an image.
Why do denser parts look more dark on the image of a TEMs?
They absorb more electrons.
Magnification-
Resolution-
Can be seen-
Cannot be seen-
Living or dead-
Colour-
Cost-
x1500
200nm
whole cell & organelles
smaller than nucleus
living & dead
full colour/stained
relatively cheap
Magnification-
Resolution-
Can be seen-
Cannot be seen-
Living or dead-
Colour-
Cost-
500,000+
0.1nm
all parts of the cell
nothing
dead only
black & white (ra salts)
very expensive
What is the eyepiece graticule?
EP of OM, no units.
What is a stage micrometer?
Used to calibrate the scale on the EG at each magnification.
what is magnification
how many times bigger the image produced is than the real object
what is the resolution
the ability to distinguish between close together objects as two separate structures
describe how a transmission electron microscope works
a beam of electrons is passed through the specimen, some parts absorb electrons due to being more dense so appear darker and others allow electrons to pass through so appear lighter
explain the advantages of a transmission electron microscope
they can produce high resolution images which allows internal structures to be seen
explain the disadvantages of TEMs
the specimens must be extremely thin for the electrons to pass through
the system must be in a vacuum so living specimens cannot be observed
lengthy sample preparation time can introduce artefacts
the image produced will never be coloured even after a long staining process
explain how scanning electron microscopes work
the beam of electrons is directed onto the surface of the specimen from above and it bounces off the surface to form a pattern
this produces a 3D image
explain the disadvantages of the SEMs
they work on a lower resolution than transmissions
cannot observe live specimens
do not produce a colour image
explain the advantages of SEMs
they can be used on thick 3D specimens
allow the external 3D structure to be observed
why do optical microscopes have a limited resolution
because it is impossible to resolve two objects close than half the wavelength of light
