Biol 1 - Microscopes

Revision notes on microscopes, aqa AS biology unit one

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  • Created by: Stephanie
  • Created on: 12-05-12 14:45

Terms

Magnification:

  • how much bigger the image is then the specimen
  • magnification = length of image / length of specimen

Resolution:

  • how detailed the image is - how well it distinguishes between two points
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Light Microscopes

  • Use Light
  • Low resolution
  • Low magnification
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Electron Microscopes

  • Uses electron to form an image
  • Shorter wave length
  • higher resolution
  • higher magnification
  • can't be use on live specimens
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Transmission Electron Microscopes (TEM)

  • Electromagnets used to focuz a beam of electrons on specimen
  • Denser parts absorb more and appear darker (like xrays)
  • Gives high resolution
  • Can only be used on thin specimens
  • Specimens have to be specially prepared in a vaccuum
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Scanning Electron Microscopes (SEM)

  • Scan a beam of electrons over sample
  • knocks off electrons collected in a cathode ray tube to make image
  • shows surface of specimen & can be 3D
  • can be used on thick specimens
  • lowere resolution than TEM
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