Microscopy

• Define resolution

  The smallest distance between 2 objects that can be distinguished - how much detail can be seen in the image.
• Role of a microscope

  Designed to magnify smaller objects, so they appear larger.
• How does a microscope work ?

  Light from a mirror (or light source) passes through a specimen, objective lens, the eyepiece lens, and into your eye.
• What is the magnifying power of a light microscope ?

  X 2000
• Main Disadvantages of light microscopes

  • Light microscopes rely on light, whereas electron microscopes rely on electrons
  • Light has a much longer wavelength than electron, which means that light microscopes have a lower resolution than electron microscopes
  • Means light microscopes have a lower maximum magnification, and so can’t see many detail within cells e.g. sub-cellular structures
• Why do electron microscopes have a greater magnification and resolution than light microscopes ?

  • They use a beam of electrons rather than light waves, and the electrons have a shorter wavelength than light waves.
• What is the magnifying power of an electron microscope ?

  X 2000000
• 5 disadvantages of electron microscopes (compared to light microscopes ?

  • Expensive
  • Difficult to use, require specialist training.
  • Large, difficult to transport
  • Images generated are in black and white .
  • Can only view dead specimens
• Main advantage of electron microscopes ?

  • Have a greater resolution and magnification
  • Means they can be used to see details within sub-cellular structures.
• 5 advantages of light microscopes (compared to electron microscopes)

  
  

  • Cheap
  • Easy to use
  • Small , easy to transport
  • Produce colour images
  • Can see live cells
• How many nm are there in 1 µm ?

  1000
• Arrange units for microscopy smallest - largest

  • nm
  • um
  • mm
  • cm
  • m
  • km
• Roughly how large is an animal cell

  100 µm wide
• How many mm in 1cm ?

  10
• Equation for magnification

  Magnification = image size ÷ object size
• Rearrange magnification equation to make image size the subject.

  Image size = object size ÷ magnification
• Rearrange the magnification equation to make object size the subject

  Object size = image size ÷ magnification
• Equation for total magnification

  eyepiece magnification x objective lens magnification