Microscopes Flashcards
compound microscopes use white or blue light
white
the magnifying lenses of a compound microscope include (2)
- objective (4,10 and 40x)
- eyepiece (10x)
the resolving power of the compound microscope is
0.2 um
the resolving power of an electron microscope is
0.001 um
what is the light source of an electron microscope
beam of high speed electrons
how are the lenses of an electron microscope different from compound light microscope
they are magnetic
what are two types of electron microscopes
- TEM transmission electron microscope
- SEM scanning electron microscope
how does a TEM work
- beam of electrons passes through sample that has been embedded in resin
- the specimen absorbs or scatters electrons
- remaining electrons focused onto fluorescent screen or photographic plate by the magnetic lenses
how can the fine details of specimens be improved in TEM
by staining (heavy metal salt)
how does SEM work
- the electron beam is focused so that it strikes a small spot on a dehydrated spcimen that has been coated with a thin layer of gold
- specimen surface is scanned
- electrons are scattered off of the sample (secondary electrons)
- secondary electrons control intensity of beam in a detector resulting in topographical map of specimen
the light source for fluorescent microscopy is
- short wave UV, violet or blue light (around 350 nm)
- usually xenon vapour or mercury arc lamps
excitation filters are inserted before or after the condenser, why
before to cut the UV spectrum down to a narrow band
why is a barrier filter applied gehind the objective
to allow observation by the human eye such that not damaged by UV rays
what is the principle of fluorescence microscopy
- some substances can fluoresce when exposed to short wavelengths of light
- need to contain either natural fluorescence or be stained with dilute dyes
