Microscopes

• Types of microscopes

  • Optical (light) microscopes
  • Transmission electron microscope
  • Scanning electron microscope
• Magnification


  How many times larger the image is compared to the object
• Resolution

  The minimum distance between two objects in which they can be viewed as separate
• Resolution in an optical microscope

  Determined by the wavelength of light
• Resolution in an electron microscope

  Determined by the wavelength of the beam of electrons
• Optical (light) microscopes

  • A beam of light is condensed to create the image
  • Poorer resolution due to light having a longer wavelength
  • Lower magnification
  • Coloured images
  • Can view living samples
  • Small organelles are not visible
• Electron microscopes

  • A beam of electrons is condensed to create the image, electromagnets used to condense the beam
  • Higher resolving power as electrons have a short wavelength
  • Higher magnification
  • Black and white images
  • Sample must be in a vacuum because the electrons are absorbed by air, so non living
• Transmission electron microscopes

  • Extremely thin specimens stains and placed in a vacuum
  • An electron gun produces a beam of electrons that pass through the specimen
  • Some parts absorb electrons and appear dark
  • 2D image showing detailed images on internal structures of cells
• Scanning electron microscopes

  • Specimens don't need to be thin as electrons are not transmitting through
  • Electrons beamed onto the surface and scattered in different ways depending on the contours
  • 3D image
• Magnification


  image size / actual size
• Units of measurement

  • metres
  • millimetre
  • micrometre
  • nanometre
• Eyepiece graticule


  A scale on a glass disc inside optical microscopes, used to measure the size of objects viewed
• Calibrating the eyepiece graticule


  1. Line up the stage micrometer and eyepiece graticule

  2. Count how many decisions on the eyepiece graticule fit into one division on the micrometer scale

  3. Calculate what one decision on the eyepiece graticule is at that current magnification
• One division on a micrometer is 10. If 2 divisions from eyepiece graticule fit into 1 division on micrometer, so 10/2 then one division on the eyepiece graticule is 5 micrometres at this magnification