Magnification

• Magnification of a microscope

  The magnification of the eyepiece lens multiplied by the magnification of the objective lens
• Magnification of a photograph (or a drawing)

  Photographs and drawings of cells observed using a microscope are almost always much larger than the size of the image observed, so the overall magnification will be usually greater than the magnification down the microscope alone
• Calculating actual size (length) of a cell or structure

  1. size (length) of Image = Actual size (length) x Magnification

  2. actual size = size of image / magnification
• Micrometre

  The unit of measurement usually used to measure cells. There are one million micrometres in a metre and one thousand micrometres in a millimetre.
• Units

  • Millimetre (mm)
  • Micrometre (μm)
• Using a scale bar

  A scale bar gives the actual length of a section of a photograph (or drawing). Scale bars are normally used for calculating the magnification.
• Calculating magnification using a scale bar

  magnification = size of scale bar / actual size
• Calculating actual cell length using magnification and image length

  actual length = image length / magnification
• Students are expected to be able to estimate sizes where appropriate
• Electron microscopes

  • Beams of electrons rather than beams of light pass through the specimen to form an image
  • Allow much greater resolution than light microscopes (up to x500,000 magnification compared to x1,500 for light microscopes)
  • Allow us to see structures and internal cell details that were previously not visible
• Resolution

  The ability of a microscope to preserve detail when magnifying. The ability to see two separate points as distinct entities.