microscopes

• Light microscopes and electron microscopes are the two main types of microscopes
• Light Microscope:

  • Specimen is placed on a slide with a cover slip on top to make it flat
  • Specimen should be thin to allow light to pass through
  • Light is shone through the specimen from below
  • Stain can be used to enhance visibility of different parts of the specimen
  • Parts of the microscope:
  • Eyepiece: where you look in
  • Objective: multiple objectives for changing magnification
  • Stage: where the slide is placed
  • Focusing knob: moves the stage up and down to bring the specimen into focus
  • Light source: usually a light bulb underneath the stage
• Electron Microscope:

  • A beam of electrons is fired at the specimen
  • Electrons pass through the specimen and are detected
  • A computer produces an image based on how the electrons were scattered by the specimen
  • Provides much higher magnification and resolution compared to light microscopes
• Magnification Equation:

  • Magnification (m) = size of the image (i) / actual size (a)
  • Example: if actual size is 0.1 mm and size of the image is 20 mm, magnification would be 200
  • Size of the image is determined by the scale on the eyepiece graticule, usually calibrated
  • Common units: 1 mm = 1 x 10^-3 m, 1 micrometer (μm) = 1 x 10^-6 m
• Electron Microscope Advantages:

  • Much greater magnification compared to light microscopes
  • Can see inside cells and observe organelles
• Electron Microscope Disadvantages:

  • Very expensive
  • Requires special training to use
  • Can only examine dead material due to the high-energy electrons used