The Microscope

• Light microscopes magnify up to x2000

  
• What should you do first when using a microscope without a built-in light?

  Place it near a lamp or window
• Why do you move the mirror when using a microscope?

  To direct light through the stage hole
• What should be on the slide you are using?

  An object you want to look at
• How do you secure the slide on the microscope?

  Clip it to the stage
• Which objective lens should you select first?

  The lowest powered objective lens
• What should you do after selecting the lowest powered objective lens?

  Turn the rough focusing knob down
• When should you stop moving the objective lens down?

  When it's just above the slide
• What should you look through to see the image of the slide?

  The eyepiece lens
• What should you do if the image is not clear?

  Turn the fine focusing knob
• How can you make the image larger when using a microscope?

  Use a higher powered objective lens
• What steps should you repeat after changing to a higher powered objective lens?

  Refocus the microscope
• Light Microscopes

  • Developed in the mid 17th century.
  • Use a beam of light to form an image of an object. 
  • They are relatively cheap.
  • Can be used almost anywhere.
  • Can magnify live specimens.
• Electron Microscope

  • Invented in the 1930s.
  • Allowed biologists to understand more about the subcellular structures inside the cells.
  • Uses a beam of electrons to form an image.
  • Can magnify objects up to 2 000 000 times.
• Transmission Electron Microscope

  • These can give 2D images with very high magnification and resolution.
• Scanning Electron Microscope

  • These microscopes give dramatic 3D images but lower magnifications.
• Electron Microscopes

  Electron microscopes are;

  1. Large
  2. Very expensive
  3. Kept in rooms with a special temperature, pressure and humidity.
• Resolving Power

  • Light microscopes have a resolving power of 200nm.
  • Scanning electron microscopes have a resolving power of 10nm.
  • Transmission electron microscope has a resolving power of 0.2nm.
• Calculations: Object size / Real Size?

  Size of real object = Size of image

                                     Magnification

  Example

  With a magnification of 200, the size of image was 20mm

  Size of real object = 20mm

  200

  Size of real object = 0.1mm
• The limits of the light microscope

  very low magnifications are not possible with the light micrascope. This is because of the electron-gathering ability of the microscope and short working distances of high power lenses. the highest magnification is X150.

  Using higher magnifecation does always mean that you can see greater detail in an image. This depends on the resolving power, or resolution. This is the ability to distinguish between two cells. The resolving power of a light microscope is 0.2nm.
• Magnification Equation

  Magnification= image size ÷ actual size
• Example of Magnification Equation

  A cell has a diameter of 0.001cm. An image of that cell seen through the microscope has a diameter of 5 cm.

  Magnification = 5 cm ÷ 0.001 cm = x5000
• A cell has a diameter of 0.002cm. An image of the cell viewed through the microscope has a diameter of 6 cm. What is the magnification?

  x3000